U.S. patent number 7,043,271 [Application Number 09/660,467] was granted by the patent office on 2006-05-09 for radio communication system.
This patent grant is currently assigned to Kabushiki Kaisha Toshiba. Invention is credited to Hidehiro Matsuoka, Yasushi Murakami, Ichiro Seto, Osamu Shibata.
United States Patent |
7,043,271 |
Seto , et al. |
May 9, 2006 |
Radio communication system
Abstract
There is disclosed a radio communication system in which a
constitution of a base station and further a control station can be
simplified. A radio communication system according to the present
invention converts a received signal received by a plurality of
antenna elements in a base station to a signal of different
frequency band, and then conflates the converted signal in order to
generate sub-carrier wave multiplex signal. The signal is converted
to an optical signal, and then the optical signal is transmitted to
a control station via an optical fiber. Or the control station
performs weighting to phase of the transmitted signal transmitted
from a plurality of antennas of a base station, and then performs
frequency conversion to different frequency band, and then
conflates the converted signal in order to generate the sub-carrier
wave multiplex signal. The signal is converted to an optical
signal, and then an optical signal is transmitted to the base
station side via the optical fiber. The control station and the
base station divides the received sub-carrier wave multiplex signal
by each frequency band, and then the frequency of the divided
signals are converted to the same frequency band in order to
generate the transmitted/received signal of each antenna element.
By such a constitution, it is possible to reduce constituent of the
optical transmission components to the minimum and to simplify the
constitution of the base station. Furthermore, it is possible to
maintain the relative phase difference and the relative intensity
of the transmitted/received signal of each antenna element. Because
of this, it is possible to estimate an arrival direction of the
received signal and to control radiation beam pattern of the
transmitted signal.
Inventors: |
Seto; Ichiro (Fuchu,
JP), Murakami; Yasushi (Yokohama, JP),
Shibata; Osamu (Kawasaki, JP), Matsuoka; Hidehiro
(Yokohama, JP) |
Assignee: |
Kabushiki Kaisha Toshiba
(Kawasaki, JP)
|
Family
ID: |
27478500 |
Appl.
No.: |
09/660,467 |
Filed: |
September 12, 2000 |
Foreign Application Priority Data
|
|
|
|
|
Sep 13, 1999 [JP] |
|
|
11-259137 |
Sep 13, 1999 [JP] |
|
|
11-259346 |
Sep 13, 1999 [JP] |
|
|
11-259355 |
Sep 24, 1999 [JP] |
|
|
11-271124 |
|
Current U.S.
Class: |
455/562.1;
455/561; 398/58 |
Current CPC
Class: |
H04B
7/0617 (20130101); H04B 7/086 (20130101); H04W
88/08 (20130101); H01Q 3/2676 (20130101); H04B
10/25753 (20130101); H01Q 3/2605 (20130101); H04J
14/02 (20130101); H04J 14/0298 (20130101); H04B
17/20 (20150115); H04B 17/10 (20150115) |
Current International
Class: |
H04M
1/00 (20060101) |
Field of
Search: |
;455/561,562.1,277.1,277.2,272,63.4,25,132,134,524,525
;398/58,41,43 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0 391 597 |
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Oct 1990 |
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EP |
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0 685 973 |
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Dec 1995 |
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EP |
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0 843 380 |
|
May 1998 |
|
EP |
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2 255 881 |
|
Nov 1992 |
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GB |
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2 331 667 |
|
May 1999 |
|
GB |
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9-23209 |
|
Jan 1997 |
|
JP |
|
9-70062 |
|
Mar 1997 |
|
JP |
|
9-215047 |
|
Aug 1997 |
|
JP |
|
10-145286 |
|
May 1998 |
|
JP |
|
10-248087 |
|
Sep 1998 |
|
JP |
|
Other References
US. Appl. No. 09/310,198, Unknown. cited by other .
U.S. Appl. No. 09/243,121, filed Feb. 3, 1999, pending. cited by
other .
U.S. Appl. No. 09/329,574, filed Jun. 10, 1999, pending. cited by
other .
U.S. Appl. No. 09/660,467, filed Sep. 12, 2000, pending. cited by
other.
|
Primary Examiner: Urban; Edward F.
Assistant Examiner: Bhattacharya; Sam
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier
& Neustadt, P.C.
Claims
What is claimed is:
1. A radio communication system comprising a base station for
performing radio communication with a radio communication terminal;
and a control station connected to the base station via an optical
transmission line, said base station comprising: a variable
direction array antenna which comprises a plurality of antenna
elements and which can change directivity in accordance with a
position of said radio communication terminal; a base station side
frequency conversion unit configured to subject received signals
received from said radio communication terminal via said plurality
of antenna elements to frequency conversion to different bands; a
sub-carrier multiplexing signal generation unit configured to
combine a plurality of signals subjected to the frequency
conversion by said base station side frequency conversion unit to
generate a sub-carrier multiplexing signal; and a base station side
transmission means configured to transmit optical signals generated
by conducting optical modulation with respect to said sub-carrier
multiplexing signal to said control station via said optical
transmission line, said control station comprising: a first
optical/electric conversion unit configured to convert the optical
signal transmitted from said base station into an electric signal;
a first branching unit configured to branch the electric signal to
the signals received by the plurality of antennas; control station
side frequency conversion unit configured to perform the frequency
conversion to obtain the signals of the same frequency band for
each of the branched signals; a beam calculation unit configured to
obtain a weighting coefficient to control directivity of said
plurality of antenna elements; a weighting unit configured to
perform weighting with respect to the branched signals of which
frequencies have been converted by said control station side
frequency conversion unit based on said weighting coefficient; a
combiner unit configured to combine the weighted signals; and a
received signal generation unit configured to demodulate the
combined signals to generate a received signal.
2. The radio communication system according to claim 1 wherein said
base station further comprises: a first local oscillator for
supplying a first reference signal as a frequency conversion
reference to said base station side frequency conversion unit, said
control station further comprises: a second local oscillator for
supplying a second reference signal as the frequency conversion
reference to said control station side frequency conversion unit,
and said second local oscillator outputs said second reference
signal which has a predetermined phase relation with said first
reference signal so that said control station side frequency
conversion unit output the signal maintaining a relative phase
difference among the respective received signals of said plurality
of antenna elements.
3. The radio communication system according to claim 1 wherein said
base station comprises: a reference signal generation unit
configured to generate a reference signal; and a reference signal
transmission unit configured to directly transmit the generated
reference signal for superposing the reference signal to said
sub-carrier multiplexing signal and transmitting the signal to said
control station, and said base station side frequency conversion
unit and said control station side frequency conversion unit
perform the frequency conversion based on the same reference signal
generated by said reference signal generation unit.
4. The radio communication system according to claim 1 wherein said
control station comprises: an addition unit configured to superpose
a signal correlated with the transmitted signal transmitted to said
radio communication terminal from said variable direction antenna
and a signal correlated with said weighting coefficient; and
control station side transmission means configured to transmit the
signal superposed by said addition means to said base station, said
base station comprises: a second branching unit configured to
branch the signal converted with the transmitted signal included in
the signal transmitted from the control station to a number equal
to a number of said antenna elements, and detect a weighting
control signal correlated with the weighting coefficient; and a
base station side weighting unit configured to weight the signals
correlated with said transmitted signal branched by said second
branching unit based on the weighting control signal; wherein said
antenna elements transmit the respective signals subjected to the
base station side weighting unit to said radio communication
terminals.
5. The radio communication system according to claim 1 wherein said
base station comprises: a second optical/electric conversion unit
configured to convert an optical signal transmitted from said
control station via said transmission line to an electric signal; a
separation unit configured to separate the electric signal
converted by the second optical/electric conversion means to the
transmitted signal for said radio communication terminal and a beam
control signal for controlling the radiation beam-pattern of said
variable direction antenna; an antenna control unit configured to
control the radiation beam-pattern of a transmission/reception beam
of said variable direction antenna based on said beam control
signal; a base station side transmission frequency conversion unit
configured to convert the transmitted signals for said radio
communication terminal separated by said separation unit to a radio
frequency signal and supply the radio frequency signal to said base
station side transmission unit, and a radio transmission control
unit which transmits transmission signals for said radio
communication terminal via the variable direction antenna to said
radio communication terminal said control station comprises: a
level detection unit configured to detect a maximum intensity
and/or an intensity distribution of the signals subjected to the
frequency conversion by said control station side frequency
conversion unit, and generating said beam control signal based on
the detection result; a control station side frequency multiplexing
unit configured to multiplex the transmitted signal for said radio
communication terminal and said beam control signal; and an second
electric/optical conversion unit configured to optically modulate
the signal multiplexed by said control station side frequency
multiplexing unit to generate said optical signal, and the first
optical signal to said base station via said optical transmission
line.
6. The radio communication system according to claim 1 wherein said
base station comprises: a second optical/electric conversion unit
configured to convert an optical signal transmitted from said
control station via said transmission line to an electric signal; a
separation unit configured to separate the electric signal
converted by the second optical/electric conversion unit to the
transmitted signal for said radio communication terminal and a beam
control signal for controlling the radiation beam pattern of said
variable direction antenna; and received signal selection unit
configured to select some signals from signals correlated with the
respective received signals received from said radio communication
terminal via said plurality of antenna elements based on said beam
control signal, and said sub-carrier multiplexing signal generation
unit multiplexes only the signals selected by said received signal
selection means.
7. The radio communication system according to claim 1 wherein said
base station comprises the variable direction antenna constituted
of first to n-th antenna elements (n is a positive integer), at
least one of said base station and said control station comprises a
phase compensation unit configured to compensate a phase
fluctuation amount generated by a signal propagation path between
said base station and said control station, and a signal processing
on the side of said base station and said control station, and said
phase compensation unit establishes a relation
.phi..sub.1+2m.sub.1.pi.=.phi..sub.2+2m.sub.2.pi.=.phi..sub.3+2m.sub.3.pi-
.= . . . =.phi..sub.n+2m.sub.n.pi. (m.sub.1, . . . , m.sub.n are
integers) in respective phase change amounts .phi..sub.1 to
.phi..sub.n in blocks of said antenna elements disposed on said
base station and said weighting unit disposed on said control
station with respect to the received signal of said variable
direction antenna.
8. The radio communication system according to claim 1, wherein
said base station side frequency conversion unit generates a
frequency-converted signal obtained by converting the signals
weighed by said weighting unit to frequencies different from each
other based on a plurality of local oscillation signals with
frequencies different from each other, and said sub-carrier
multiplexing signal generation unit generates the sub-carrier
multiplexing signal obtained by multiplexing the frequency-convened
signal and the plurality of local oscillation signals.
9. A radio communication system comprising a base station including
a variable direction array antenna which has a plurality of antenna
elements and which can change directivity in accordance with a
position of a radio communication terminal; and a control station
connected to the base station via an optical transmission line,
said control station comprising: a control station side branching
unit configured to branch a signal correlated with a transmitted
signal transmitted to said radio communication terminal from said
variable direction antenna for said plurality of antenna elements;
a weighting unit configured to weight based on a weight control
signal with respect to the signals of the respective antenna
elements relating to the transmitted signal transmitted from said
variable direction antenna to said radio communication terminal; a
control station side frequency conversion unit configured to
convert frequencies of the signals weighted by said weighting unit
to respective different bands; a sub-carrier multiplexing signal
generation unit configured to combine the respective signals
converted to the different bands subjected to the frequency
conversion by said control station side frequency conversion unit
to generate a sub-carrier multiplexing signal; and a transmission
unit configured to transmit optical signals generated by conducting
optical modulation with respect to said sub-carrier multiplexing
signal to said base station via said optical transmission line,
said base station comprising: a base station side branching unit
configured to convert the optical signals transmitted from said
base station via said optical transmission line to electric
signals, and branch the electric signals for said plurality of
antenna elements; and a base station side frequency conversion unit
configured to subject the respective signals branched by said base
station side branching unit to the signals of the same frequency
band, wherein said plurality of antenna elements transmit the
respective signals subjected to the frequency conversion by said
base station side frequency conversion unit to said radio
communication terminal.
10. The radio communication system according to claim 9 wherein
said base station further comprises: a first local oscillator for
supplying a first reference signal as a frequency conversion
reference to said base station side frequency conversion unit, said
control station further comprises: a second local oscillator for
supplying a second reference signal as the frequency conversion
reference to said control station side frequency conversion unit,
and said second local oscillator outputs said second reference
signal which has a predetermined phase relation with said first
reference signal so that said control station side frequency
conversion unit output the signal maintaining a relative phase
difference among the respective received signals of said plurality
of antenna elements.
11. The radio communication system according to claim 9 wherein
said control station comprises: a reference signal generation unit
configured to generate a reference signal; and a reference signal
transmission unit configured to directly transmit the generated
reference signal for superposing the reference signal to said
sub-carrier multiplexing signal and transmitting the signal to said
base station, and said base station side frequency conversion unit
and said control station side frequency conversion unit perform the
frequency conversion based on the same reference signal generated
by said reference signal generation unit.
12. The radio communication system according to claim 9 wherein
said base station comprises the variable direction antenna
constituted of first to n-th antenna elements (n is a positive
integer), at least one of said base station and said control
station comprises phase compensation unit configured to compensate
a phase fluctuation amount generated by a signal propagation path
between said base station and said control station, and a signal
processing on the side of said base station and said control
station, and said phase compensation unit establishes a relation
.phi..sub.1+2m.sub.1.pi.=.phi..sub.2+2m.sub.2.pi.=.phi..sub.3+2m.sub.3.pi-
.= . . . =.phi..sub.n+2m.sub.n.pi. (m.sub.1, . . . , m.sub.n are
integers) in respective phase change amounts .phi..sub.1 to
.phi..sub.n in blocks of said antenna elements disposed on said
base station and said weighting unit disposed on said control
station with respect to the transmitted signal to said variable
direction antenna.
13. The radio communication system according to claim 9, wherein
said control station side frequency conversion unit generates a
frequency-converted signal obtained by converting the signals
weighed by said weighting unit to frequencies different from each
other based on a plurality of local oscillation signals with
frequencies different from each other, and said sub-carrier
multiplexing signal generation unit generates the sub-carrier
multiplexing signal obtained by multiplexing the
frequency-converted signal and the plurality of local oscillation
signals.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a radio communication system which
is constituted of a base station equipped with a variable
beam-pattern array antenna such as an adaptive array antenna, and a
control station connected to the base station via an optical fiber
and which is provided with a function of controlling the variable
beam-pattern array antenna on the side of the control station.
2. Related Background Art
Much attention has been paid to a radio on fiber (ROF) technique of
connecting a base station and a control station for mobile
communication represented by cellular phones and intelligent
transport systems (ITS) to each other by an optical fiber in order
to perform signal transmission. According to the ROF technique, a
radio signal is transmitted from the base station to the control
station via an optical fiber, and a modulator/demodulator, a
controller and the like are collectively contained in the control
station in order to simplify and miniaturize a constitution of base
station. Therefore, it is possible to arrange a plurality of base
stations along a road, in an underground shopping center, in a
tunnel, and the like.
Moreover, in order to solve problems such as tightness of a
frequency band in the base station, and an interference wave, an
adaptive antenna capable of varying directivity has been noted. The
adaptive antenna is provided with an array antenna having a
plurality of antenna elements, and the radiation beam-pattern of
the antenna can be changed by transmitted signals transmitted from
the respective antenna elements.
A beam calculation circuit in the control station derives a
radiation pattern of a radio signal to a subscriber from the base
station, and the radiation pattern of the radio signal to the base
station from the subscriber, and changes the radiation beam-pattern
of the adaptive antenna in an adaptive manner in accordance with
movement and position of the subscriber.
Several reports on a radio communication system, in which the base
station is provided with this type of adaptive antenna and which is
connected to the control station by using the ROF technique, have
been published (e.g., Japanese Patent Application Laid-open No.
145286/1998).
FIGS. 1 and 2 are block diagrams schematically showing a
constitution of the radio communication system utilizing the ROF
technique. In consideration of a transmission/reception function as
the radio communication system, it is most important to transmit
the radio signal received by each antenna element to the control
station from the base station while a relative phase difference and
a relative intensity difference are maintained.
Therefore, in the conventional system, a transmitted/received
signal of each antenna element is converted to a optical signal,
and then transmitted between the base station and the control
station by multiplexing a wavelength, or by allotting a specific
optical fiber to each antenna element.
In the conventional system utilizing the ROF technique, however, as
shown in FIGS. 1 and 2, a pair of an electric/optical converter and
an optical/electric converter are allotted to each antenna element
line, and the base station and control station require pairs of
optical transmitter/receiver by the number of antenna elements.
Therefore, elements constituting optical transmitters of the base
station and the control station largely increase, the constitution
is complicated and an apparatus becomes large-sized. Moreover, when
wavelength multiplexing transmission is performed, an optical
multiplexer, an optical branching filter, a wavelength control
function of a light source, and other constitutions are further
necessary.
On the other hand, if the optical fiber is provided by each antenna
element, the number of optical fibers for connecting the base
station to the control station largely increases, and accordingly
the constitutions of optical transmitters such as the
optical/electric converter and the electric/optical converter
become complicated and large-sized.
Thus, in the conventional radio communication system, provided with
the adaptive antenna, for utilizing the ROF technique to perform
the signal transmission, since there are many constituting elements
for the optical transmitter, the constitution is complicated, it is
difficult to miniaturize the base station and control station, and
cost cannot be reduced.
SUMMARY OF THE INVENTION
The present invention has been developed in consideration of these
respects, and an object thereof is to provide a radio communication
system in which a constitution of a base station and a control
station can be simplified and miniaturized without deteriorating a
transmission quality.
Moreover, another object of the present invention is to provide a
reliable radio communication system which can easily and precisely
adjust phase and amplitude of a transmitted signal transmitted to a
base station from a control station without complicating a
constitution.
To attain the aforementioned objects, there is provided an up link
from a terminal side to an infrastructure side in a radio
communication system comprising a base station for performing radio
communication with a radio communication terminal; and a control
station connected to the base station via an optical transmission
line,
said base station comprising:
a variable beam-pattern array antenna which comprises a plurality
of antenna elements and which can change directivity in accordance
with a position of said radio communication terminal;
base station side frequency conversion means configured to subject
received signals received from said radio communication terminal
via said plurality of antenna elements to frequency conversion to
different bands;
sub-carrier multiplexing signal generation means configured to
combine a plurality of signals subjected to the frequency
conversion by said base station side frequency conversion means to
generate a sub-carrier multiplexing signal; and
base station side transmission means configured to transmit said
sub-carrier multiplexing signal to said control station via said
optical transmission line,
said control station comprising:
control station side frequency conversion means configured to
branch said sub-carrier multiplexing signal transmitted from said
base station via said optical transmission line to signals received
by said plurality of antenna elements, and performing the frequency
conversion to obtain the signals of the same frequency band for
each of the branched signals;
beam calculation means configured to obtain a weighting coefficient
to control directivity of said plurality of antenna elements;
weighting means configured to perform weighting based on said
weighting coefficient; and
received signal generation means configured to generate the
received signal by combining said branched signals that frequency
is converted by said control station side frequency conversion
means and weighting is performed.
Moreover, there is provided a down link from an infrastructure side
to a terminal side in a radio communication system comprising: a
base station comprising a variable beam-pattern array antenna which
comprises a plurality of antenna elements and which can change
directivity in accordance with a position of a radio communication
terminal; and a control station connected to the base station via
an optical transmission line,
said control station comprising:
control station side branching means configured to branch a signal
correlated with a transmitted signal transmitted to said radio
communication terminal from said variable beam-pattern array
antenna for said plurality of antenna elements;
weighting means configured to weight based on a weight control
signal for the signals of the respective antenna elements relating
to the transmitted signal transmitted from said variable
beam-pattern array antenna to said radio communication
terminal;
control station side frequency conversion means configured to
convert frequency to respective different bands;
sub-carrier multiplexing signal generation means configured to
combine the respective signals converted to the different bands
subjected to the frequency conversion by said control station side
frequency conversion means to generate a sub-carrier multiplexing
signal; and
transmission means configured to transmit said sub-carrier
multiplexing signal to said base station via said optical
transmission line,
said base station comprising:
base station side branching means configured to branch said
sub-carrier multiplexing signal transmitted from said control
station via said optical transmission line for said plurality of
antenna elements; and
base station side frequency conversion means configured to subject
the respective signals branched by said base station side branching
means to the signals of the same frequency band, wherein
said plurality of antenna elements transmit the respective signals
subjected to the frequency conversion by said base station side
frequency conversion means to said radio communication
terminal.
According to the present invention, since the signals received by
the plurality of antenna elements are converted to the sub-carrier
multiplexing signal, and transmitted optically between the control
station and the base station, the constitution of the signal
transmitter between the base station and the control station can be
simplified.
According to the present invention, each of a transmitter and a
receiver can transmit a signal by one piece of the optical fiber,
respectively. Because of this, only one pair of an electric/optical
converter and a optical/electric converter is necessary to each of
the transmitter and the receiver without depending on the number of
the antenna elements. Accordingly, the following advantageous
effects are obtained.
First, it is possible to reduce the number of the optical fiber
more than that of a conventional fiber multiple system.
Furthermore, the optical transmitter of the present invention does
not need an optical multiplexer unit and an optical demultiplexer,
different from the wave length multiple system, and the
electric/optical converter does not need a wave length control
circuit. It is possible to reduce a constitution of the optical
transmission parts more than the radio communication system using
the conventional fiber multiplex and wavelength division multiplex
systems because the system on the present invention requires one
pair of the electric/optical converter and the optical/electric
converter, simplifies and miniaturizes constitutions of the control
station and the base station to a large degree. It is possible to
reduce cost of the base station by reducing the number of optical
transmission components that cost is higher than electrical
components.
Furthermore, according to the present invention, applying
phase-locked loop techniques or transmission of said sub-carrier
multiplexing signal with local oscillator signals to the
above-mentioned radio communication systems, it is possible to
maintain in principle relative phase difference of the
transmitted/received signal of the antenna element provided with
the base station, even if the effective length changes by the
peripheral temperature's change. Therefore, it is possible to
estimate arrival direction of the received signal in the beam
calculation circuit of the control station side. It is possible to
control beam pattern forming of the array antenna of the base
station side. That is, it is unnecessary to dispose the beam
calculation circuit and the control circuit on the base station
side. It is possible to constitute of passive components and to
miniaturize the overall constitution. Even when a large number of
base stations provided with these advantages are arranged in a
broad area, a highly reliable and highly stable radio communication
system can be provided.
In the above-mentioned radio communication system according to the
present invention, there is a system of applying a beam forming
network and level detecting means. The radio communication system
of applying such a system comprising:
a base station provided with a variable directional array antenna
whose directivity changes by an electric signal for supplying power
to a plurality of antenna elements; and
a control station provided with a signal calculation circuit for
performing weighting of electric signal applied to said plurality
of antenna elements,
said base station being connected to said control station via an
optical transmission line,
wherein the electric signal for supplying the power to said
plurality of antenna elements is transmitted to said base station
from said control station via said optical transmission line,
and
the signal transmitted via said optical transmission line is
constituted by multiplexing an electric signal obtained by
subjecting the electric signal for supplying the power to said
plurality of antenna elements to frequency conversion to different
frequencies by a plurality of local oscillator outputs different in
frequency from one another.
Moreover, there is a radio communication system comprising:
a base station provided with an array antenna including a plurality
of antenna elements; and
a control station provided with a beam forming network for deriving
a desired signal from a received signal of said variable
directional array antenna,
said base station being connected to said control station via an
optical transmission line,
wherein an electric signal received by said plurality of antenna
elements is transmitted to said control station from said base
station via said optical transmission line, and
the signal transmitted via said optical transmission line is
constituted by multiplexing an electric signal obtained by
subjecting the electric signal received by said plurality of
antenna elements to frequency conversion to different frequencies
by a plurality of local oscillator outputs different in frequency
from one another.
Moreover, there is provided a radio communication system comprising
a base station for performing radio communication with a radio
communication terminal; and a control station connected to the base
station via an optical transmission line, wherein
said base station comprises:
a plurality of antenna elements different in directivity from one
another;
first optical/electric conversion means configured to convert a
first optical signal transmitted from said control station via said
optical transmission line to an electric signal;
separation means configured to separate the electric signal
converted by the first optical/electric conversion means to a
transmitted signal for said radio communication terminal and an
antenna selection signal for selecting said plurality of antenna
elements;
antenna control means configured to select any one of said
plurality of antenna elements based on said antenna selection
signal to control the antenna element;
transmission means configured to transmit the transmitted signal
for said radio communication terminal to the radio communication
terminal via said antenna element;
first frequency multiplexing means configured to subject signals
correlated with respective received signals received from said
radio communication terminal via said antenna element to frequency
multiplexing; and
first electric/optical conversion means configured to optically
modulate the signal subjected to the frequency multiplexing by the
frequency multiplexing means to generate a second optical signal,
and transmitting the second optical signal to said control station
via said optical transmission line, and said control station
comprises:
second optical/electric conversion means configured to convert said
second optical signal transmitted from said base station to the
electric signal;
demultiplex means configured to divide the electric signal
converted by said second optical/electric conversion means to said
plurality of frequency signals before multiplexing;
weighting means configured to weight the signals correlated with
the respective frequency signals divided by said demultiplex means
with respect to a phase and/or a signal intensity;
combiner means configured to synthesize the respective signals
weighted by said weighting means;
demodulation means configured to demodulate the received signal
based on the signal synthesized by said combiner means;
level detection means configured to detect a maximum intensity
and/or an intensity distribution of the signals correlated with the
respective frequency signals divided by said demultiplex means, and
generating said antenna selection signal based on the detection
result;
second frequency multiplexing means configured to multiplex the
transmitted signal for said radio communication terminal with said
antenna selection signal; and
second electric/optical conversion means configured to optically
modulate the signal multiplexed by said second frequency
multiplexing means to generate said first optical signal, and
transmitting the first optical signal to said base station via said
optical transmission line.
According to the present invention having the beam forming network,
when the received signal is transmitted from the base station to
the control station, a maximum intensity and/or an intensity
distribution of the received signal in the base station or the
control station are detected, and based on the detecting result,
the radiation beam-pattern of the transmitted signal addressed to
the radio communication terminal is controlled. Because of this, it
is unnecessary to transmit the received signal while maintaining
the relative phase difference from the base station to the control
station, thereby simplifying and miniaturizing constitutions of the
base station and the control station.
Furthermore, when the control station generates a control signal
for controlling directivity of the transmitted signal addressed to
the radio communication terminal in the base station, if the
control signal is transmitted to the base station by multiplexing
the transmitted signal addressed to the radio communication
terminal, it is possible to simplify the constitution of the
transmitter.
Moreover, when the base station generates a control signal for
controlling directivity of the transmitted signal addressed to the
radio communication terminal, the control station may send only the
transmitted signal addressed to the radio communication terminal.
Because of this, it is possible to simplify the constitution of the
transmitter.
Furthermore, when only necessary received signal is transmitted
from the base station to the control station based on the maximum
intensity and/or the intensity distribution, it is possible to
reduce the number of the received signal transmitted to the control
station, and to simplify the constitution of the receiver.
Moreover, the radio communication system according to the present
invention also includes means configured to compensate the relative
phase difference between the antenna elements in the base station.
There is a radio communication system including the means
comprising a radio communication terminal; a base station for
performing radio communication with the radio communication
terminal; and a control station connected to the base station via
an optical transmission line,
said base station comprising:
an array antenna comprising a plurality of antenna elements;
and
feedback means configured to feed respective transmitted signals
corresponding to said antenna elements transmitted from said
control station via said optical transmission line back to said
control station via said optical transmission line,
said control station comprising:
comparing detection means configured to compare at least two
signals among said respective transmitted signals fed back from
said feedback means, and detecting a phase difference and/or an
amplitude fluctuation amount; and
compensation means configured to compensate for the respective
transmitted signals corresponding to said plurality of antenna
elements based on the phase difference and/or the amplitude
fluctuation amount detected by said comparing detection means.
According to the present invention, since the transmitted signal
transmitted to the base station from the control station is fed
back to the control station, and the phase and amplitude of the
transmitted signal are adjusted based on the comparison result of
the transmitted signal with the fed back signal, or the comparison
result of two of the fed back signals, the phase difference and
amplitude fluctuation amount generated during propagation of the
transmitted signal in the control station and base station can
easily and precisely be calibrated.
Moreover, according to the present invention, since a calibration
processing can be performed even during communication, the
communication is not interrupted by the calibration.
As mentioned above, the radio communication system according to the
present invention can reduce the number of the electric/optical
converters and the optical/electric converters of the control
station and the base station to a large degree. Accordingly, it is
possible to miniaturize the constitutions of the base station and
the control station. By reduction of the optical components, it is
possible to reduce cost of the radio communication system. By such
an advantage, it is possible to allocate many base stations,
thereby enlarging the communication area.
Furthermore, the radio communication system according to the
present invention can restrain fluctuation of the relative phase
difference between the antenna elements even if an effective length
changes by fluctuation of the peripheral temperature in the optical
fiber of the transmitted line possibly arranged outside. Because of
this, it is possible to stabilize operation of the system and to
realize the radio communication system with high reliability.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram schematically showing a radio
communication system utilizing an ROF technique.
FIG. 2 is a block diagram schematically showing a radio
communication system utilizing the ROF technique.
FIG. 3 is a block diagram schematically showing a first embodiment
of the radio communication system according to the present
invention.
FIG. 4 is a block diagram showing a base station local
oscillator.
FIG. 5 is a waveform diagram of a base station LO signal.
FIG. 6A is a diagram showing input/output signals of a multiplier
and a band pass filter, and FIG. 6B is a diagram showing the
input/output signals of the multiplier and band pass filter.
FIG. 7A is a waveform diagram of a received signal when a relation
of equation (14) is not satisfied, and FIG. 7B is a waveform
diagram of the received signal when the relation of equation (14)
is satisfied.
FIG. 8 is a block diagram of a second embodiment of the radio
communication system according to the present invention.
FIG. 9 is a block diagram showing a detailed constitution of a
control station local oscillator of FIG. 8.
FIG. 10 is a frequency spectrum diagram of a sub-carrier
multiplexing signal generated by a coupler.
FIG. 11 is a block diagram showing a detailed constitution of a
base station local oscillator.
FIG. 12 is a block diagram of a third embodiment of the radio
communication system according to the present invention.
FIG. 13 is a block diagram showing a fourth embodiment of the radio
communication system according to the present invention.
FIG. 14A is a frequency spectrum diagram of the received signal,
FIG. 14B is a frequency spectrum diagram of a spread spectrum
signal, and FIG. 14C is a frequency spectrum diagram of a spread
spectrum multiple signal.
FIG. 15A is a block diagram showing a detailed constitution of a
spread spectrum unit, and FIG. 15B is a block diagram showing a
detailed constitution of a de-spread spectrum unit.
FIG. 16 is a block diagram of a fifth embodiment of the radio
communication system according to the present invention.
FIG. 17 is a block diagram of a sixth embodiment of the radio
communication system according to the present invention.
FIG. 18 is a block diagram of a seventh embodiment of the radio
communication system according to the present invention.
FIG. 19 is a block diagram of an eighth embodiment of the radio
communication system according to the present invention.
FIG. 20 is a frequency spectrum diagram of respective signals
inputted to the coupler in the control station.
FIG. 21 is a diagram showing a connection relation of a distributor
and a band pass filter in the base station.
FIG. 22 is a block diagram of a ninth embodiment of the radio
communication system according to the present invention.
FIG. 23 is a block diagram of a tenth embodiment of the radio
communication system according to the present invention.
FIG. 24 is a block diagram of an eleventh embodiment of the radio
communication system according to the present invention.
FIG. 25 is a block diagram of a twelfth embodiment of the radio
communication system according to the present invention.
FIG. 26 is a block diagram schematically showing the radio
communication system of the present invention.
FIGS. 27A and 27B are diagrams showing properties of beams formed
by a beam forming network.
FIG. 28 is a block diagram of a fourteenth embodiment of the radio
communication system according to the present invention.
FIG. 29A is a diagram schematically showing beam formation in a
directional antenna of FIG. 3, and FIG. 29B is a diagram
schematically showing the beam formation by the element antenna and
beam forming network of FIG. 26.
FIG. 30 is a block diagram of a fifteenth embodiment of the radio
communication system according to the present invention.
FIG. 31 is a block diagram of a sixteenth embodiment of the radio
communication system according to the present invention.
FIG. 32 is a block diagram of a seventeenth embodiment of the radio
communication system according to the present invention.
FIG. 33 is a diagram showing that in a circuit of FIG. 31, a
directional antenna is connected instead of an array antenna.
FIG. 34 is a block diagram of an eighteenth embodiment of the radio
communication system according to the present invention.
FIG. 35 is a frequency spectrum diagram of a signal subjected to
antenna element multiplexing in a combiner.
FIG. 36 is a block diagram showing a detailed constitution of a
calibration coefficient calculation circuit.
FIG. 37 is a block diagram showing a detailed constitution of a
phase difference detector.
FIG. 38 is a block diagram showing a detailed constitution of an
amplitude ratio detector.
FIG. 39 is a diagram showing a signal intensity of a pilot
signal.
FIG. 40 is a block diagram of a nineteenth embodiment of the radio
communication system according to the present invention.
FIG. 41 is a block diagram of a twentieth embodiment of the radio
communication system according to the present invention.
FIG. 42 is a block diagram of a twenty first embodiment of the
radio communication system according to the present invention.
FIG. 43 is a block diagram of the radio communication system in
which FIG. 41 is modified.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A radio communication system according to the present invention
will concretely be described hereinafter with reference to the
drawings. Additionally, in the following embodiments, in order to
show a principle phase state and signal intensity state,
dispersions of gain, loss, transmittance, and group speed by solid
differences of microwave components such as an amplifier, a
multiplier, and a filter inserted into each antenna element line
and a delay difference by a line length are ignored.
First Embodiment
FIG. 3 is a block diagram schematically showing a constitution of a
first embodiment of the radio communication system according to the
present invention. The radio communication system of FIG. 3 is
constituted of a base station 1 and a control station 2, and the
stations are connected to each other via an optical fiber 3.
The base station 1 has array antennas 4a to 4d constituted of four
antenna elements, low noise amplifiers 5a to 5d, a base station
local oscillator (first local oscillator) 6, multipliers (base
station side frequency conversion means) 7a to 7d, band pass
filters 8a to 8d, a coupler (sub-carrier multiplexing signal
generation means) 9, and an electric/optical converter (E/O
converter: base station side transmission means) 10.
The control station 2 has an optical/electric converter (O/E
converter) 11, a divider 12, a control station local oscillator
(second local oscillator) 13, multipliers (control station side
frequency conversion means) 14a to 14d, band pass filters 15a to
15d, a beam calculation circuit (beam calculation means) 16,
weighting circuits (weighting means) 17a to 17d, a coupler
(received signal generation means) 18, and a demodulator 19.
In the base station 1, a radio signal 70 from a subscriber (not
shown) is received by the array antennas 4a to 4d. In the present
embodiment, a case in which the number of elements of the array
antennas 4 is four (the respective elements 4a to 4d are shown in
FIG. 3) will be described, but the number of elements is not
particularly limited. Received signals 71a to 71d received by the
respective array antennas 4a to 4d are represented by an equation
(1).
.function..times..function..omega..times..PHI..function..PHI..times..time-
s..function..times..function..omega..times..PHI..function..PHI..times..tim-
es..function..times..function..omega..times..PHI..function..PHI..times..ti-
mes..function..times..function..omega..times..PHI..function..PHI.
##EQU00001##
In the equation (1), the radio signal 70 is a phase modulation
signal such as quadriphase-shift keying (QPSK), and a phase
modulation term is .phi..sub.m(t). Additionally, t denotes time,
.omega. denotes a signal angular frequency, .phi. denotes each
signal relative phase, P denotes each signal relative intensity,
and signal types are distinguished by affixed characters. Affixed
characters a to d show that signals are related with respective
antenna elements a to d. As shown in the equation (1), the
respective received signals 71a to 71d change in phase and
amplitude in accordance with an arrival direction of the radio
signal 70.
The received signals 71a to 71d are inputted to the multipliers 7a
to 7d via the low noise amplifiers 5a to 5d. The multipliers 7a to
7d multiply signals passing through the low noise amplifiers 5a to
5d by base station LO signals 72a to 72d outputted from the base
station local oscillator 6, and convert down the frequency. The
base station LO signals 72a to 72d are represented by equation
(2).
.function..times..times..function..omega..times..times..PHI..times..times-
..times..function..times..times..function..omega..times..times..PHI..times-
..times..times..function..times..times..function..omega..times..times..PHI-
..times..times..times..function..times..times..function..omega..times..tim-
es..PHI..times. ##EQU00002##
The base station LO signals 72a to 72d are, as shown in the
equation (2), equal to one another in power and different from one
another in frequency. By performing multiplication with the base
station LO signals 72a to 72d, the received signals 71a to 71d are
converted to signals of a low frequency band with frequencies
different from each other.
The outputs of the multipliers 7a to 7d are inputted to the band
pass filters 8a to 8d, and desired band received signals 73a to 73d
are extracted. The received signals 73a to 73d are represented by
equation (3).
'.function..times..times..times..times..times..omega..omega..times..times-
..PHI..function..PHI..PHI..times..times..times.'.function..times..times..t-
imes..times..times..omega..omega..times..times..PHI..function..PHI..PHI..t-
imes..times..times.'.function..times..times..times..times..times..omega..o-
mega..times..times..PHI..function..PHI..PHI..times..times..times.'.functio-
n..times..times..times..times..times..omega..omega..times..times..PHI..fun-
ction..PHI..PHI..times. ##EQU00003##
The received signals 73a to 73d passing through the band pass
filters 8a to 8d are combined by the coupler 9, and a sub-carrier
multiplexing signal 74 is generated. The generated sub-carrier
multiplexing signal 74 is inputted to the electric/optical
converter 10, converted to a optical signal 150, and transmitted to
the control station 2 via the optical fiber 3.
The optical signal transmitted to the control station 2 via the
optical fiber 3 is converted to a received signal 75 by the
optical/electric converter 11 such as a photo detector (PD). The
received signal 75 is distributed by the number of antenna elements
by the divider 12, and subsequently inputted to the multipliers 14a
to 14d.
The multipliers 14a to 14d multiply an output signal of the divider
12 by base station LO signals 76a to 76d outputted from the control
station local oscillator 13, and perform frequency conversion. The
control station LO signals 76a to 76d are, as shown in the equation
(4), equal to one another in power, and different from one another
in frequency, and by performing multiplication with these signals,
the frequency of the received signal 75 subjected to sub-carrier
wave multiplexing is again converted to the same frequency band in
the control station 2.
.function..times..times..function..omega..times..times..PHI..times..times-
..times..function..times..times..function..omega..times..times..PHI..times-
..times..times..function..times..times..function..omega..times..times..PHI-
..times..times..times..function..times..times..function..omega..times..tim-
es..PHI..times. ##EQU00004##
Outputs of the multipliers 14a to 14d are inputted to the band pass
filters 15a to 15d, and desired band received signals 77a to 77d
are extracted. The received signals 77a to 77d are represented by
equation (5).
''.function..times..times..times..times..times..times..times..times..omeg-
a..omega..times..omega..times..times..times..PHI..function..PHI..PHI..time-
s..PHI..times.''.function..times..times..times..times..times..times..times-
..times..omega..omega..times..omega..times..times..times..PHI..function..P-
HI..PHI..times..PHI..times.''.function..times..times..times..times..times.-
.times..times..times..omega..omega..times..omega..times..times..times..PHI-
..function..PHI..PHI..times..PHI..times.''.function..times..times..times..-
times..times..times..times..times..omega..omega..times..omega..times..time-
s..times..PHI..function..PHI..PHI..times..PHI..times.
##EQU00005##
Here, respective frequencies and phases of the output signals 72a
to 72d of the base station local oscillator 6 and the output
signals 76a to 76d of the control station local oscillator 13 are
set to satisfy conditions of equations (6) and (7) =--=--=--=-- (6)
k+2m.pi.=.phi..sub.1a+.phi..sub.2a+2m.sub.a.pi.=.phi..sub.1b+.phi..sub.2b-
2m.sub.b.pi.=.phi..sub.1c+.phi..sub.2c+2m.sub.c.pi.=.phi..sub.1d+.phi..sub-
.2d+2m.sub.d.pi. (7)
When the conditions of the equations (6) and (7) are satisfied, the
received signals 77a to 77d represented by the equation (5) are
rewritten as in equation (8).
''.function..times..times..function..omega..times..PHI..function..PHI..ti-
mes..times.''.function..times..times..function..omega..times..PHI..functio-
n..PHI..times..times.''.function..times..times..function..omega..times..PH-
I..function..PHI..times..times..times..times.''.function..times..times..fu-
nction..omega..times..PHI..function..PHI. ##EQU00006##
As seen from comparison of the equation (1) with the equation (8),
the received signals 77a to 77d maintain relative phase differences
.phi..sub.a to .phi..sub.d and relative intensities Pa to Pd of the
received signals 71a to 71d in the base station 1. Therefore,
influences of phase addition and signal intensity fluctuation
during propagation of the received signal to the control station 2
from the base station 1 can be ignored.
The beam calculation circuit 16 performs calculation for
controlling signal processings such as optimum synthesis based on
the received signals 77a to 77d. When it is unnecessary for the
radio communication system as an object to obtain the arrival
direction of the radio signal 70, the beam calculation circuit 16
may perform only the optimum synthesis. In this case, the condition
of equation (7) does not have to be necessarily satisfied.
The beam calculation circuit 16 in the present embodiment partially
takes the received signals 77a to 77d, and calculates phase and
intensity weights to perform the optimum signal synthesis.
Subsequently, based on the calculation results, by controlling the
weighting circuits 17a to 17d, adding the phase and signal
intensity weights to the received signals 77a to 77d, and combining
the respective signals by the multiplexer 18, a received signal 78
is obtained. The received signal 78 is inputted to the demodulator
19, and information from the subscriber is extracted.
The beam calculation circuit 16, in addition to the aforementioned
signal processing, based on the relative phase differences .phi.a
to .phi.d and relative intensity differences Pa to Pd, can perform
optimum multiplexing control with respect to a delay wave, or
restrain an unnecessary wave and an interference wave of the
received signal and perform signal-to-interference ratio (SIR)
optimum multiplexing. Moreover, the arrival direction of the radio
signal 70 can also be obtained by calculation.
In the present embodiment, a transmitter to the subscriber from the
base station 1 is not shown, but estimation of the arrival
direction of the radio signal 70 in the control station 2 is
important for determining the transmission direction of the radio
signal to the subscriber from the base station 1, and the
calculation result of the beam calculation circuit 16 can be
applied to the transmitter.
In principle, when the respective signal intensities of the base
station LO signals 72a to 72d and control station LO signals 76a to
76d are constant, it is possible to transmit the signal to the
control station 2 while holding the relative intensity difference
of the received signal 71a to 71d. Similarly, it is possible to
transmit the signal from the control station 2 to the base station
1. Hereinafter, no relative intensity difference is not referred
to, and the relative phase difference is noted.
The received signals 71a to 71d of the respective antenna elements
4a to 4d are transmitted to the control station 2 from the base
station 1 with different carrier wave frequencies. When the carrier
wave frequency is different, the relative phase difference between
the antenna element lines changes in accordance with propagation
time. Therefore, it is necessary to consider a relation of phase
terms of the base station LO signals 72a and 72d and control
station LO signals 76a to 76d used in two frequency conversions in
total in the base station 1 and control station 2.
FIG. 4 is a block diagram showing a constitution of the base
station local oscillator 6. As shown in FIG. 4, the base station
local oscillator 6 has a reference oscillator 20, distributor 21,
phase comparators 22a to 22d, voltage control oscillators (VCO) 23a
to 23d, frequency dividers 24a to 24d, and loop filters 25a to
25d.
A highly stable oscillator such as a crystal is used in the
reference oscillator 20. An oscillation frequency of an output
signal 80 of the reference oscillator 20 is set to fr. The output
signal 80 is divided by the number of antenna elements by the
distributor 21, and inputted to the phase comparators 22a to
22d.
Signals 81 obtained by dividing frequencies of output signals 72a
to 72d from the VCO 23a to 23d, for example, to N, (N+1), . . . ,
(N+3) are inputted to phase comparators 22a to 22d. The phase
comparators 22a to 22d compare the phases of two input signals 80,
81 with each other, and output a phase comparison signal 82. The
phase comparison signal 82 is fed back to the VCO 23a to 23d via
the loop filters 25a to 25d. By this feedback, the frequencies of
the base station LO signals 72a to 72d as outputs of the VCO 23a to
23d are locked in order of N.times.fr, (N+1).times.fr,
(N+2).times.fr, (N+3).times.fr.
FIG. 5 is a waveform diagram of the base station LO signals 72a to
72d. The actually outputted oscillation signals 72a to 72d are
sinusoidal waves, but here rectangular waves are shown in order to
clarify rising and falling phase states, a rising phase is set to
zero degree, and a falling phase is set to .pi. degree.
FIG. 5 shows waveforms of the base station LO signals 72a to 72d
when the phase comparator 21 outputs the phase comparison signal 82
so that a phase difference between the reference oscillator output
signal 80 and the frequency division signal 81 is 0 degree, and the
base station LO signals 72a to 72d are represented by equations
shown in FIG. 5.
The control station local oscillator 13 on the side of the control
station 2 is constituted similarly as the base station local
oscillator 6 and generates the control station LO signals 76a to
76d. The oscillation frequency of the reference signal 80 in the
control station local oscillator 13 is fr, which is the same as
that on the side of the base station 1. Moreover, the frequencies
of the control station LO signals 76a to 76d are locked in order of
(N+3).times.fr, (N+2).times.fr, (N+1).times.fr, N.times.fr so that
the frequencies of the received signals 77a to 77d coincide with
each other.
Here, it is assumed that a phase state of reference signal 80 on
the base station 1 side is .phi..sub.BS, and the phase state of the
reference signal 80 on the control station 2 side is .phi..sub.CS.
In order to show a phase change amount to the received signal 77
from the received signal 71, the received signal 71a represented by
the equation (1) is rewritten as in equation (9).
Ra(t)=cos[.omega..sub.RFt] (9)
Moreover, when the phase state of the reference signal 80 is
.phi.BS, the base station LO signal 72a of the equation (2) can be
rewritten as follows. LO1a(t)=cos[N.omega..sub.rt+N+.phi..sub.BS]
(10)
FIG. 6A is a diagram showing input/output signals of the multiplier
7a and band pass filter 8a, and FIG. 6B is a diagram showing the
input/output signals of the multiplier 14a and band pass filter
15a. From the aforementioned equations (9) and (10), the received
signal 73a outputted from the band pass filter 8a can be
represented as in equation (11).
R'a(t)=(1/2).times.cos[(.omega..sub.RF-N.omega..sub.r)t-N.phi..sub.-
BS] (11)
The propagation time of the received signal 73 to the control
station 2 from the base station 1 is set to T, and t'=t-T. On the
control station 2 side, the received signal 75 transmitted from the
base station 1 (here, only the desired band of the line of the
antenna element 4a is shown) is multiplied by the control station
LO signal 76a. When the phase state of the reference signal 80 on
the control station 2 side is .phi..sub.CS, the control station LO
signal 76a can be represented by equation (12).
LO2a(t)=cos[(N+3).omega..sub.rt'+(N+3).phi..sub.CS] (12)
The frequencies of the control station LO signals 76a to 76d are
selected to convert the received signals 75a to 75d to the same
frequency band. Therefore, briefly, the frequencies of the control
station LO signals 76a to 76d may be set to (N+3).omega.r,
(N+2).omega..sub.r, (N+1).omega..sub.r, N.omega. in order.
As described above, the received signal 77a can be represented by
equation (13).
'.function..times..times..function..omega..times..times..omega..times..om-
ega..times.'.times..times..PHI..times..PHI..times..times..function..omega.-
.times.'.times..times..PHI..times..PHI..times..times..function..omega..tim-
es..omega..times..times..times..PHI..times..PHI. ##EQU00007##
In the equation (13), an added phase term to the received signal
77a from the received signal 72a is
-.omega..sub.IFT-N.phi..sub.BS-(N+3).phi..sub.CS. The added phase
terms to the other received signals 77b to 77d can similarly be
obtained. When -.omega..sub.IFT as a common part to the respective
phase terms is omitted, the added phase terms to the received
signals 77b to 77d are -(N+1).phi..sub.BS-(N+2).phi..sub.CS,
-(N+2).phi..sub.BS-(N+1).phi..sub.CS,
-(N+3).phi..sub.BS-N.phi..sub.CS in order. When these added phase
terms are equal, the relative phase difference to the respective
received signals 71a to 71d are also kept in the received signals
77a to 77d. For this purpose, .phi..sub.CS and .phi..sub.BS need to
satisfy a relation of equation (14).
.phi..sub.CS=.phi..sub.BS.+-.2.pi. (14)
By satisfying the relation of the equation (14), each added phase
term is -(2N+3).phi..sub.BS.+-.2.pi., and the relative phase
difference added to the received signals 77a to 77d is zero.
Here, to check the influence by the added phase term, the received
signals 71a to 71d are sinusoidal signals with a relative phase
difference of zero. When the relation of the equation (14) is not
satisfied, for the received signals 77a to 77d, as shown in FIG.
7A, the added phase terms in two frequency conversions differ among
the lines of the respective antenna elements 4a to 4d, the relation
of the relative phase difference collapses, and no waveform is
overlapped.
On the other hand, when the relation of the equation (14) is
satisfied, the added phase term by the two frequency conversions is
equal. Therefore, when it is supposed that the received signals 71a
to 71d are sinusoidal signals with a relative phase difference of
zero, the waveform of the received signals 77a to 77d in the
control station 2 is as shown in FIG. 7B. In this case, since the
added phase term by the two frequency conversions is equal, the
waveforms of the received signals 77a to 77d are all
coincident.
As described above, in the first embodiment, since the received
signals received by the plurality of antenna elements 4a to 4d in
the base station 1 are subjected to sub-carrier wave multiplexing
and transmitted to the control station 2, the constituting elements
of the optical transmitter part can be minimized, and the
constitution of the base station 1 can be simplified. Moreover,
while the relative phase difference and relative intensity of the
respective received signals are maintained, the received signals
can be transmitted to the control station 2 from the base station
1, so that high-quality signal reception is possible without being
influenced by unnecessary and interference waves.
Second Embodiment
In a second embodiment, a reference signal outputted from the base
station local oscillator 6 and a reference signal outputted from
the control station local oscillator 13 are shared.
FIG. 8 is a block diagram of the second embodiment of the radio
communication system according to the present invention. In FIG. 8,
constituting parts common to FIG. 3 are denoted by the same
reference numerals, and respects different from FIG. 3 will mainly
be described hereinafter.
In the radio communication system of FIG. 8, the constitution of a
receiver to the control station 2 from the base station 1 is
similar to that of the first embodiment except the constitutions of
the base station local oscillator 6 and control station local
oscillator 13.
The radio communication system of FIG. 8 is characterized in that
the constitution of the transmitter to the base station 1 from the
control station 2 is newly added, and the base station local
oscillator 6 and control station local oscillator 13 use a common
reference signal to generate a local oscillator output.
The newly added transmitter in the base station 1 has an
optical/electric converter 31, distributor (second branching means)
32, multipliers (fourth frequency conversion means) 33a to 33d,
band pass filters 34a to 34d, low noise amplifiers 35a to 35d, and
circulators 36a to 36d for switching transmission/reception.
Moreover, the newly added transmitter in the control station 2 has
a modulator (MOD) 41, distributor (first branching means) 42,
weighting circuits (weighting means) 43a to 43d, multipliers
(control station side frequency conversion means) 44a to 44d, band
pass filters 45a to 45d, coupler (sub-carrier multiplexing signal
generation means) 46, and electric/optical converter (transmission
means) 47.
FIG. 9 is a block diagram showing a detailed constitution of the
control station local oscillator 13 of FIG. 8. As shown in FIG. 9,
the control station local oscillator 13 has reference oscillator 20
for outputting a reference signal, distributor 21, phase
comparators 22a to 22d, voltage control oscillators (VCO) 23a to
23d, frequency dividers 24a to 24d, band pass filters 25a to
25d.
The distributor 21 distributes the reference signal outputted from
the reference oscillator 20 more than the number of antenna
elements. Subsequently, the reference signal 80 subjected to no
signal processing is inputted to the coupler 9 in the control
station 2 shown in FIG. 8.
Transmitted signals 87a to 87d transmitted to the base station 1
from the control station 2 will be described later in detail. The
reference signal 80 is combined with the transmitted signals 87a to
87d by the coupler 9, and transmitted as a sub-carrier multiplexing
signal 88 to the base station 1.
FIG. 10 is a frequency spectrum drawing of the sub-carrier
multiplexing signal 88 generated by the coupler 9. The sub-carrier
multiplexing signal 88 is converted to a optical signal 151 by the
electric/optical converter 10, and optically transmitted to the
base station 1 from the control station.
The optical/electric converter 11 in the base station 1 converts
the optical signal 151 transmitted from the control station 2 to a
received signal 89. The received signal 89 is inputted to the
divider 12, and distributed to the antenna element line and base
station local oscillator 6.
FIG. 11 is a block diagram showing a detailed constitution of the
base station local oscillator 6. When the received signal 89 from
the distributor 21 of FIG. 9 passes through a band pass filter 26
of FIG. 11, the desired reference signal 80 is obtained. The base
station local oscillator 6 generates the base station LO signals
72a to 72d for the respective antenna element lines based on the
reference signal transmitted from the control station 2. Thereby,
the reference signal 80 of the control station local oscillator 13
and base station local oscillator 6 can be shared.
An operation of the transmitter in the second embodiment will next
be described. An intermediate frequency signal S.sub.IF(t) as an
output from the modulator 26 in the control station 2 is
represented by equation (15).
.function..times..function..omega..PHI..function. ##EQU00008##
In the equation (15), similarly as the first embodiment, it is
supposed that radio signals 91 transmitted from the antenna
elements 4a to 4d are phase modulation signals such as
quadriphase-shift keying (QPSK), phase modulation term is
.phi..sub.m(t), intermediate frequency is .omega..sub.IF, and
signal power is P.sub.IF.
An intermediate frequency signal 85 outputted from the modulator 16
of FIG. 8 is branched by the distributor 42 by the number of
antenna elements, and the respective signals are inputted to the
weighting circuits 43a to 43d. Moreover, the beam calculation
circuit 16 extracts the relative phase difference and relative
intensity difference from the received signals 76a to 76d which
have the relative phase difference and relative intensity
difference equal to those of the received signals 71a to 71d.
The arrival direction of the radio signal 70, that is, a
subscriber's position is detected from the extracted information,
the transmission direction of the radio signal 91 is determined
based on the position, and the corresponding weight is calculated.
The weighting circuits 43a to 43d add the amplitude and phase, or
the phase weight to the intermediate frequency signal 85 in
accordance with the weight control from the beam calculation
circuit 16. When the weight is represented by W, output signals 86a
to 86d of the weighting circuits 43a to 43d are represented by
equation (16).
'.function..times..times..function..omega..times..PHI..function..PHI..tim-
es..times..times..times.'.function..times..times..function..omega..times..-
PHI..function..PHI..times..times..times..times.'.function..times..times..f-
unction..omega..times..PHI..function..PHI..times..times..times..times.'.fu-
nction..times..times..function..omega..times..PHI..function..PHI..times..t-
imes. ##EQU00009##
The weighting signals 86a to 86d of the equation (16) are
multiplied by the control station LO signals 76a to 76d from the
control station local oscillator 13 shown in the equation (4) by
the multipliers 44a to 44d. Outputs of the multipliers 44a to 44d
are inputted to the band pass filters 45a to 45d, the desired band
is extracted, and the transmitted signals 87a to 87d arranged in
different frequencies are obtained. Equation (17) represents Sa''
(t) to Sd'' (t) as the obtained transmitted signals 87a to 87d.
''.function..times..times..times..times..times..times..omega..omega..time-
s..times..PHI..function..PHI..times..times..PHI..times..times..times.''.fu-
nction..times..times..times..times..times..times..omega..omega..times..tim-
es..PHI..function..PHI..times..times..PHI..times..times..times.''.function-
..times..times..times..times..times..times..omega..omega..times..times..PH-
I..function..PHI..times..times..PHI..times..times..times.''.function..time-
s..times..times..times..times..times..omega..omega..times..times..PHI..fun-
ction..PHI..times..times..PHI..times. ##EQU00010##
The transmitted signals 87a to 87d are combined with the reference
signal 80 from the control station local oscillator 13 by the
coupler 9, and the sub-carrier multiplexing signal 88 is obtained.
The sub-carrier multiplexing signal 88 is converted to the optical
signal 151 in the electric/optical converter 47, and transmitted to
the base station 1 via the optical fiber 3.
On the base station 1 side, the optical/electric converter 31 such
as PD converts the optical signal to the received signal 89 as the
electric signal. The received signal 89 is branched by the divider
32, and inputted to the antenna element line and base station local
oscillator 6.
As described above, the base station local oscillator 6 generates
the base station LO signals 72a to 72d shown in the equation (2)
based on the reference signal 80 on the control station 2 side. In
the antenna element line, the received signal 89 is multiplied by
the base station LO signals 72a to 72d from the base station local
oscillator 6, and the frequencies of the respective received
signals are converted to the same radio frequency band
.omega..sub.RF.
Outputs of the multipliers 33a to 33d are inputted to the band pass
filters 34a to 34d and the desired band is extracted. Outputs of
the band pass filters 34a to 34d are passed through the power
amplifiers 35a to 35d and circulators 36a to 36d, and transmitted
signals 90a to 90d to be supplied to the antenna elements 4a to 4d
are obtained. These transmitted signals 90a to 90d are represented
by equation (18).
.function..times..times..times..times..times..times..times..times..times.-
.omega..omega..times..omega..times..times..times..PHI..function..PHI..time-
s..times..PHI..times..PHI..times..function..times..times..times..times..ti-
mes..times..times..times..times..omega..omega..times..omega..times..times.-
.times..PHI..times..PHI..times..times..PHI..times..PHI..times..function..t-
imes..times..times..times..times..times..times..times..times..omega..omega-
..times..omega..times..times..times..PHI..times..PHI..times..times..PHI..t-
imes..PHI..times..function..times..times..times..times..times..times..time-
s..times..times..omega..omega..times..omega..times..times..times..PHI..tim-
es..PHI..times..times..PHI..times..PHI..times. ##EQU00011##
Here, the frequencies and phases of the transmitted signals 90a to
90d are set to satisfy conditions of equations (19) and (29)
similarly as the first embodiment. By satisfying the constitutions
of the base station and control station local oscillators 6, 13 in
the receiver described in the first embodiment and the relation of
the equation (14), a relation of equation (20) can be obtained.
.omega..sub.RF=.omega..sub.IF+.omega..sub.1a+.omega..sub.2a=.omega..sub.I-
F+.omega..sub.1b+.omega..sub.2b=.omega..sub.IF+.omega..sub.1c+.omega..sub.-
2c=.omega..sub.IF+.omega..sub.1d+.omega..sub.2d (19)
.times..times..times..pi..times..PHI..times..PHI..times..times..times..pi-
..PHI..times..PHI..times..times..times..pi..times..PHI..times..PHI..times.-
.times..times..pi..PHI..times..PHI..times..times..times..times..pi.
##EQU00012##
Additionally, k denotes a constant, and m, m.sub.a to m.sub.d
denote integers.
From the above, the transmitted signals 90a to 90d from the
respective antenna elements 4a to 4d can be represented by equation
(21).
.function..times..times..function..omega..times..PHI..function..PHI..time-
s..times..times..times..function..times..times..function..omega..times..PH-
I..function..PHI..times..times..times..times..function..times..times..func-
tion..omega..times..PHI..function..PHI..times..times..times..times..functi-
on..times..times..function..omega..times..PHI..function..PHI..times..times-
. ##EQU00013##
In a variable directional array antenna of an adaptive control, it
is important to add weights of amplitude and phase to the signals.
Moreover, for the phase, a relative phase relation is important,
and there is no problem even when a fixed phase component k is
included.
The transmitted signals 90a to 90d are subjected to the weighting
of amplitude and phase by the beam calculation circuit 16 of the
control station 2, and a radiation pattern of the radio signal 91
radiated from the antenna elements 4a to 4d is controlled. When the
transmitted signals 90a to 90d radiated from the antenna elements
4a to 4d of the base station 1 are combined in a subscriber's
direction in the same phase, the radio signal 91 received by the
subscriber is represented by equation (22).
.function.'.times..function..omega..times..PHI..function.'
##EQU00014##
Character k' denotes a phase constant term including delay by
propagation, and Ps' denotes a signal power with loss by
propagation.
As described above, in the second embodiment, since the reference
signal for the local oscillator output is common to both the base
station local oscillator 6 and control station local oscillator 13,
the constitution can be simplified, and mutual phase and signal
intensity deviations of the local oscillator outputs can be
eliminated.
Moreover, during transmission of the transmitted signal to the base
station 1 from the control station 2, while the relative phase
information and relative intensity information of the transmitted
signal are maintained in principle, the transmitted signal can be
transmitted to the base station 1 from the control station 2, so
that it is unnecessary to dispose the constituting element for
performing an active signal processing in the base station 1, the
base station 1 can be miniaturized, and the simple constitution can
enhance reliability.
In the second embodiment, the constitution of a down link for
multiplexing the reference signal 80 with the sub-carrier
multiplexing signal 87 and then transmitting it from the control
station 2 to the base station 1 has been described. Even in the up
link, the reference signal 80 may be multiplexed with the
sub-carrier multiplexing signal in order to transmit from the base
station 1 to the control station.
Third Embodiment
For the transmitter of the second embodiment, in order to minimize
and simplify the constitution of the base station 1, the
transmission weighting circuits (second weighting means) 43a to 43d
are disposed on the control station 2 side. The transmitted signals
87a to 87d transmitted to the base station 1 side from the control
station 2 side differ only in phase and amplitude, different from
the received signals 71a to 71d propagated in the radio propagation
line of the receiver and influenced by noise, phasing, and the
like. Therefore, the constitutions of the weighting circuits 43a to
43d can be simplified.
On the other hand, when the weighting circuits 43a to 43d can be
disposed on the base station 1 side, the intermediate frequency
signal 85 and the weighting control signal from the beam
calculation circuit 16 may be transmitted to the base station 1
side from the control station 2 side, and weighted on the base
station 1 side to generate the transmitted signal.
In a third embodiment described hereinafter, the weighting circuits
43a to 43d of the transmitter are disposed on the base station 1
side.
FIG. 12 is a block diagram of the third embodiment of the radio
communication system according to the present invention. The
constitution of the receiver is similar to that of the first and
second embodiments, and common constituting parts are denoted with
the same reference numerals.
In addition to the constitution of FIG. 8, the base station 1 of
FIG. 12 has weighting circuits 43a to 43d and a weight control
circuit 51 for performing weight control. Moreover, the control
station 2 of FIG. 12 is constituted by removing the weighting
circuits 43a to 43d from the constitution of FIG. 8.
Similarly as the first embodiment, the beam calculation circuit 16
estimates the arrival direction of the radio signal 70 based on the
phase and amplitude information of the received signals 71a to 71d
included in the sub-carrier multiplexing signal 74 from the base
station 1. From the estimated result, the radiation beam of the
radio signal 91 transmitted to the subscriber from the base station
1 is controlled by the weighting circuits 43a to 43d disposed on
the base station 1.
The beam calculation circuit 16 outputs a control signal 92 for
controlling the weights of the weighting circuits 17a to 17d on the
base station 1 side. An coupler 50 in the control station 2
superposes the weight control signal 92 and the reference signal 80
to the intermediate frequency signal 85 outputted from the
modulator 41 similarly as the second embodiment, and outputs a
transmitted signal 93.
The weight control signal 92 may take any form, but is typically a
digital signal, or a signal obtained by converting the frequency of
the digital signal to the predetermined frequency band. The
electric/optical converter 47 converts the transmitted signal 93 to
a optical signal 152, and transmits the optical signal to the base
station 1 side via the optical fiber 3.
On the base station 1 side, the optical/electric converter 31
converts the transmitted optical signal 152 to a received signal
94. The received signal 94 is branched by the divider 32, and
inputted to the lines to the antenna elements 4a to 4d, weight
control circuit 51, and base station local oscillator 6.
The weight control circuit 51 controls the weighting circuits 43a
to 43d based on the weight control signal 92, adds the weight to
the amplitude and phase of the transmitted signal 85, and outputs
intermediate frequency transmitted signals 95a to 95d.
A transmission side local oscillator 53 generates a base station LO
signal 98 as a sinusoidal wave, distributes the signal by the
number of antenna elements by a divider 12, and inputs the signals
to the respective multipliers (fourth frequency conversion means)
33a to 33d. As not shown, for the base station LO signal 98, the
base station LO signal may be generated based on the reference
signal 80 as occasion demands.
The multipliers 33a to 33d multiply the intermediate frequency
transmitted signals 95a to 95d outputted from the weight control
circuit 51 by the base station LO signal 98, and converts up the
frequency to the radio frequency band.
Outputs of the multipliers 33a to 33d are inputted to the band pass
filters 34a to 34d, the desired band is extracted, and transmitted
signals 97a to 97d are obtained via the power amplifiers 35a to 35d
and circulators 36a to 36d. The transmitted signals 97a to 97d are
inputted to the antenna elements 4a to 4d, and the radiation
pattern is changed in accordance with the subscriber's
position.
As described above, in the third embodiment, during generation of
the transmitted signals to the antenna elements 4a to 4d, since the
respective transmitted signals are weighted on the base station 1
side, the transmitted signal 85 transmitted to the base station 1
from the control station 2 may be of one type, and the constitution
on the base station 1 side can be simplified.
Moreover, since the frequency band of the base station LO signal 98
is common to the respective antenna elements 4a to 4d, the base
station local oscillator 52 may simply branch the reference signal,
and the constitution of the base station local oscillator 52 can be
simplified. Furthermore, weighting is performed in the vicinity of
the antenna elements 4a to 4d, and this prevents a disadvantage
that the phase and signal intensity fluctuate by propagation along
the transmission path after the weighting.
Fourth Embodiment
In a fourth embodiment, instead of performing the optical
transmission by subjecting the transmitted signals from the
respective antenna elements or the received signals of the
respective antenna elements to sub-carrier wave multiplexing, the
signal transmission is performed by a spread spectrum multiplex
system.
FIG. 13 is a block diagram showing a constitution of the fourth
embodiment of the radio communication system according to the
present invention. In FIG. 13, constituting parts common to the
first to third embodiments are denoted by the same reference
numerals.
The base station 1 of FIG. 13 is constituted by newly adding, to
the base station 1 of FIG. 1, spread spectrum units (first spread
spectrum multiple signal generation means) 56a to 56d for
performing spread spectrum for the received signals 71a to 71d
received at the antenna elements 4a to 4d.
Moreover, the control station 2 of FIG. 13 is provided with
de-spread spectrum units (reverse diffusion means) 57a to 57d for
performing de-spread spectrum, instead of the multipliers 14a to
14d and band pass filters 15a to 15d in the control station 2 of
FIG. 1.
An operation of the radio communication system of FIG. 13 will next
be described. The base station 1 receives the radio signal 70 from
the subscriber (not shown) via the array antennas 4a to 4d. The
received signals 71a to 71d received by the respective antenna
elements 4a to 4d are represented by the equation (1) similarly as
the first embodiment.
The respective received signals 71a to 71d differ in phase and
amplitude in accordance with the arrival direction of the radio
signal 70. The received signals 71a to 71d passing through the low
noise amplifiers 5a to 5d are multiplied by a base station LO
signal 98 outputted and branched by a base station local oscillator
54 in the multipliers 7a to 7d, and subjected to the frequency down
conversion.
Received signals 99a to 99d subjected to the frequency down
conversion are subjected to spread spectrum by the spread spectrum
units 56a to 56d. In the spread spectrum units 56a to 56d,
different spreading codes are allotted to the respective antenna
element lines. Rectangular codes such as Walsh code are preferable
for the diffusion code. The spread spectrum signals 99a to 99d
outputted from the spread spectrum units 56a to 56d are multiplexed
by the coupler 9, and a spread spectrum multiple signal 100 is
obtained.
FIG. 14A is a frequency spectrum diagram of the received signal 99,
FIG. 14B is a frequency spectrum diagram of the spread spectrum
signal 100, and FIG. 14C is a frequency spectrum diagram of a
spread spectrum multiple signal 101. The spread spectrum multiple
signal 101 is converted to a optical signal 153 by the
electric/optical converter 10, and transmitted to the control
station 2 via the optical fiber 3.
The optical/electric converter 11 of the control station 2 converts
the optical signal 153 to an electric signal 102. The electric
signal 102 is distributed by the number of antenna elements by the
divider 12, and the respective signals are inputted to the
de-spread spectrum units 57a to 57d. The de-spread spectrum units
57a to 57d perform a signal processing of de-spread spectrum with
the same spreading codes as the spreading codes allotted to the
respective antenna element lines on the base station 1 side.
Received signals 103a to 103d as outputs of the de-spread spectrum
units 57a to 57d maintain relative phase information .phi..sub.a to
.phi..sub.d and relative intensity information P.sub.a to P.sub.d
of the received signals 71a to 71d in the base station 1.
A part of the output signals 103a to 103d of the de-spread spectrum
units 33a to 33d is inputted to the beam calculation circuit 16 in
order to give the relative phase information .phi..sub.a to
.phi..sub.d and the relative intensity information P.sub.a to
P.sub.d. That is, the beam calculation circuit 16 calculates the
arrival direction of the radio signal 70 in the base station 1
based on the relative phase information .phi..sub.a to .phi..sub.d
and relative intensity information P.sub.a to P.sub.d.
Moreover, the output signals 103a to 103d of the de-spread spectrum
units 57a to 57d are inputted to the weighting circuits 17a to 17d,
weighted in phase and amplitude by the weight control signal from
the beam calculation circuit 16, and subsequently multiplexed by
the multiplexer 18 to form the received signal 78.
The beam calculation circuit 16 restrains the unnecessary wave and
interference wave with respect to the received signal 78 outputted
from the multiplexer 18, and performs weighting control of the
weighting circuits 17a to 17d so that the signal-to-interference
ratio (SIR) is optimized. The received signal 78 is inputted to the
demodulator 19, and the information from the subscriber is
extracted.
FIG. 15A is a block diagram showing a detailed constitution of the
spread spectrum unit 56, and FIG. 15B is a block diagram showing a
detailed constitution of the de-spread spectrum unit 57. As shown
in the drawings, the spread spectrum unit 56 and de-spread spectrum
unit 57 are substantially similarly constituted, and perform
multiplication of the input signal by the diffusion code.
The spread spectrum unit 56 has a multiplier 59 for multiplying the
received signal passing through the band pass filters 8a to 8d by a
diffusion code 104 from a diffusion code generator 58, and a band
pass filter 60 for extracting a desired band signal from an output
of the multiplier 59. The signal extracted by the band pass filter
60 forms the spread spectrum signal 100.
On the other hand, the de-spread spectrum unit 57 has a multiplier
62 for multiplying a reverse diffusion code 105 which is the same
as the diffusion code 104 by the received signal 102 outputted from
the divider 12, and a band pass filter 63 for extracting a desired
band from an output of the multiplier 62. The received signal 102
is subjected to de-spread spectrum by the multiplication of the
multiplier 63.
When the codes used to the spreading code 104 and the spreading
code 105 keep orthogonality for the respective antenna lines, and
adequately keep both the codes synchronization, the output of the
signal subjected to the spread spectrum with other spreading code
becomes zero, and only the desired signal is outputted from the
band pass 63.
As described above, for the lines of all the antenna elements 4a to
4d, since transmission is performed in the same frequency band, a
delay amount is equal and the relative phase difference is kept.
Furthermore, since the relative intensity difference is also kept,
on the control station 2 side, the arrival direction of the radio
signal 70 can accurately be estimated.
Moreover, with the spread spectrum multiplex system as shown in
FIG. 13, different from the sub-carrier wave multiplexing, it is
unnecessary to dispose the local oscillators corresponding to the
number of antenna elements in the base station 1, and one type of
local oscillator may only be disposed.
On the other hand, different spreading codes are necessary for the
number of antenna elements, but the diffusion code has a fixed
pattern, and the code may be stored in a memory and the like.
Therefore, the constitution of the entire base station can be
miniaturized.
In order to enhance a multiplex efficiency by spread spectrum with
respect to all the antenna elements 4a to 4d, preferably the
received signals 71a to 71d do not have a large intensity
difference. It is difficult to obtain such condition in mobile
communication, but the condition is easily satisfied in high-speed
radio communication such as wireless local loop (WLL). In the WLL,
the subscriber and base station 1 are disposed so that waves can
directly be transmitted/received, waves can directly be seen
through, and the received signals 71a to 71d received by the
respective antenna elements 4a to 4d have substantially equal
power. Therefore, the powers of the spread spectrum signals are
equal, and a high diffusion multiplex efficiency can be kept with
respect to all the antenna element lines.
Fifth Embodiment
In a fifth embodiment, by adding a transmitter to the fourth
embodiment, the spread spectrum multiplex system is also applied to
the added transmitter.
FIG. 16 is a block diagram of a fifth embodiment of the radio
communication system according to the present invention. In FIG.
16, the constituting parts common to FIG. 13 are denoted with the
same reference numerals, and different respects will mainly be
described hereinafter.
In the base station 1 of FIG. 16, as the transmitter constitution,
the optical/electric converter 31, divider 32, de-spread spectrum
units 64a to 64d, multipliers (second frequency conversion means)
33a to 33d, power amplifiers 35a to 35d, and circulators 36a to 36d
are disposed.
Moreover, in the control station 2 of FIG. 16, as the transmitter
constitution, the modulator 41, distributor 42, weighting circuits
(second weighting means) 43a to 43d, spread spectrum units 65a to
65d, coupler (addition means) 46, and electric/optical converter 47
are disposed.
The beam calculation circuit 16 calculates the radiation pattern of
the radio signal 91 to the subscriber from the base station 1 from
the relative phase difference and relative intensity difference of
the de-spread spectrum signals 103a to 103d corresponding to
received signals 107a to 107d of the base station 1.
The weighting circuits 17a to 17d on the transmitter side add the
weight to the phase and intensity of the intermediate frequency
signal 85 distributed by the number of antenna elements, and
control the radiation pattern. The transmitted signals 86a to 86d
with the weights added thereto are subjected to spread spectrum by
the spread spectrum units 65a to 65d, and subsequently multiplexed
by the coupler 46, and a spread spectrum multiple signal 108 is
obtained.
The spread spectrum multiple signal 108 is converted to a optical
signal 154 in the electric/optical converter 47, and transmitted to
the base station 1 via the optical fiber 3. On the base station 1
side, the optical/electric converter 31 such as PD converts the
optical signal 154 to a received signal 109 as the electric
signal.
The received signal 109 is branched by the divider 32, and inputted
to the respective de-spread spectrum units 64a to 64d. The
de-spread spectrum units 64a to 64d use the same reverse spreading
codes as those used in the spread spectrum units 65a to 65d to
perform de-spread spectrum. The multipliers 33a to 33d convert up
the frequency of the signal subjected to the de-spread spectrum to
the radio band frequency based on the base station LO signal 98
from the base station local oscillator 54.
Outputs of the multipliers 33a to 33d are inputted to the band pass
filters 34a to 34d, and the desired band is extracted. Thereafter,
the transmitted signals 107a to 107d to be supplied to the
respective antenna elements are obtained via the power amplifiers
35a to 35d and circulators 36a to 36d. Since the transmitted
signals 107a to 107d are weighted in amplitude and phase by the
beam calculation circuit 16 of the control station 2, the radiation
pattern of the radio signal 97 radiated from the antenna elements
4a to 4d is controlled.
As described above, in the fifth embodiment, also during
transmission of the transmitted signals to the antenna elements 4a
to 4d, since the signal transmission is performed in the spread
spectrum multiplex system, constitutions of the transmitter of the
control station and the base station can be simplified.
Sixth Embodiment
In a sixth embodiment, similarly as the third embodiment, the
transmitter weighting circuits 17a to 17d are disposed on the base
station 1 side.
FIG. 17 is a block diagram of the sixth embodiment of the radio
communication system according to the present invention. The
receiver constitution of the sixth embodiment is the same as those
of the fourth and fifth embodiments, and the same reference
numerals are used.
In addition to the constitution of FIG. 16, the base station 1 of
FIG. 17 has the weighting circuits 43a to 43d and weight control
circuit 51 for performing the weight control. Moreover, the control
station 2 of FIG. 17 is constituted by removing the weighting
circuits 43a to 43d from the constitution of FIG. 16.
Similarly as the fourth embodiment, the beam calculation circuit 16
estimates the arrival direction of the radio signal 70 based on the
phase and amplitude information of the received signals 71a to 71d
included in the spread spectrum multiple signal 74 from the base
station 1. From the estimated result, the radiation beam of the
radio signal 91 transmitted to the subscriber from the base station
1 is controlled by the weighting circuits 43a to 43d disposed on
the base station 1. The beam calculation circuit 16 outputs the
control signal 92 for controlling the weights of the weighting
circuits 43a to 43d on the base station 1 side.
The coupler 50 superposes the weight control signal 92 to the
intermediate frequency signal 85 outputted from the modulator 41,
and generates the transmitted signal 93. The weight control signal
92 may take any form, but is typically a digital signal, or a
signal obtained by converting the frequency of the digital signal
to the predetermined frequency band.
The electric/optical converter 47 converts the transmitted signal
93 to the optical signal 152, and transmits the optical signal to
the base station 1 side via the optical fiber 3. On the base
station 1 side, the optical/electric converter 31 converts the
transmitted optical signal 152 to the received signal 94. The
received signal 94 is branched by the divider 12, and inputted to
the lines to the antenna elements 4a to 4d, and weight control
circuit 51.
The weight control circuit 51 controls the weighting circuits 43a
to 43d based on the weight control signal 92, adds the weight to
the amplitude and phase of the transmitted signal 85, and generates
the intermediate frequency transmitted signals 95a to 95d. The
transmission side local oscillator 54 generates the base station LO
signal 98 as the sinusoidal wave, distributes the signal by the
number of antenna elements by a distributor 53a in order to input
the signals to the respective multipliers 33a to 33d.
The multipliers 33a to 33d multiply the intermediate frequency
transmitted signals 95a to 95d by the base station LO signal 98,
and convert the frequency. The outputs of the multipliers 33a to
33d are inputted to the band pass filters 34a to 34d, the desired
band is extracted, and the transmitted signals 97a to 97d are
obtained via the power amplifiers 35a to 35d and circulators 36a to
36d. The transmitted signals 97a to 97d are inputted to the antenna
elements 4a to 4d, and the radiation pattern of the descendent
radio signal 97 is changed in accordance with the subscriber's
position.
Seventh Embodiment
In the aforementioned first to sixth embodiments, it is assumed
that the phase condition of the equation (14) is satisfied with
respect to the phase condition of the equations (7) and (20), but
even when the condition of the equation (14) is not satisfied, the
added phase difference can be set to zero in another method.
For example, the method may have inserting a phase shifter into
some place in the line between each antenna element and the
weighting circuit, or between the local oscillator and the
multiplier of the control station or base station, applying a phase
offset to the transmitted signal or the received signal by the
inserted phase shifter, and maintaining the relative phase
difference between the antenna element lines.
FIG. 18 is a block diagram of a seventh embodiment of the radio
communication system according to the present invention, and shows
an example in which phase shifters (phase compensation means) 66a
to 66d are disposed for the respective antenna elements 4a to 4d.
The control station 2 of FIG. 18 is constituted similarly as FIG. 1
except that the phase shifters 66a to 66d are disposed between the
band pass filters 15a to 15d and the weighting circuits 17a to
17d.
By disposing the phase shifters 66a to 66d of FIG. 18, the delay
amount of the propagation line of each of the antenna elements 4a
to 4d can be compensated, and the respective antenna elements 4a to
4d maintain the received relative phase difference while the signal
can be transmitted to the control station 2 from the base station
1.
Additionally, instead of disposing the phase shifters 66a to 66d as
shown in FIG. 18, delay and phase differences among the lines of
the respective antenna elements 4a to 4d may be added as offsets to
the phase weight in the weighting circuits 17a to 17d.
In the actual radio communication system, the delay and phase
differences by individual differences are added to micro components
such as the amplifier, filter and multiplier. When the delay and
phase differences are also taken as the phase offsets into the
compensation amounts to the phase shifters 66a to 66d, or the phase
weight amounts in the weighting circuits 17a to 17d as described
above, it is possible to provide the radio communication system
with a higher reliability.
For the relation in frequency of the radio signal, intermediate
frequency signal, and LO signal, the equation (6) is used in the
first embodiment, the equation (19) is used in the second
embodiment, but equation (6a) may be used instead of the equation
(6), and equation (19a) may be used instead of the equation (19).
.omega..sub.IF=.omega..sub.RF-.omega..sub.1a+.omega..sub.2a=.omega..sub.R-
F-.omega..sub.1b+.omega..sub.2b=.omega..sub.RF-.omega..sub.1c+.omega..sub.-
2c=.omega..sub.RF-.omega..sub.1d+.omega..sub.2d (6a)
.omega..sub.RF=.omega..sub.IF+.omega..sub.1a-.omega..sub.2a=.omega..sub.I-
F+.omega..sub.1b-.omega..sub.2b=.omega..sub.IF+.omega..sub.1c-.omega..sub.-
2c=.omega..sub.IF+.omega..sub.1d-.omega..sub.2d (19a)
Specifically, either of plus and minus symbols of the frequencies
of the radio signal, intermediate frequency signal, and LO signal
may be selected.
In the aforementioned second and third embodiments, an example has
been described in which the same base station LO signals 72a to 72d
and control station LO signals 76a to 76d are used with respect to
the frequency conversion of the reception and transmitted signals
in the antennas 4a to 4d. However, for the transmission or received
signal system frequency conversion, local oscillators for
outputting different LO signals may be disposed on the control
station 2 and base station 1.
In the aforementioned embodiments, the intermediate frequency radio
signal is weighted, but the LO signal as the output of the local
oscillator 6, 13 may be weighted. Additionally, during weighting in
the LO signal, since the LO signal frequency differs with each
antenna element line in the sub-carrier wave multiplex optical
transmission of the first to third embodiments, it is preferable to
perform weighting on the state of converting the frequency of the
LO signal to the phase. Moreover, in the third and sixth
embodiments, the weighting may be performed for the transmitted
signal or the received signal of the radio frequency band such as a
front stage part of the power amplifiers 35a to 35d or a later
stage part of the low noise amplifiers 5a to 5d.
In the aforementioned embodiments, the weighting circuit for
controlling the phase and amplitude has been described as an analog
signal processing with respect to the radio signal subjected to
frequency conversion, but a digital signal processing may be
performed.
That is, in the receiver, the received signal is analog/digital
converted, and inputted to the weighting circuit as the digital
signal. Moreover, the transmitter may be constituted so that the
output of the weighting circuit as the digital signal processing is
digital/analog converted, and transmitted as the analog signal to
the base station side.
The signal synthesis method of the adaptive antenna is diversified.
In the present embodiment, the method of performing demodulation
after signal synthesis has been described, but the signal synthesis
may be performed by another method, for example, of performing
delay wave detection before the signal synthesis.
Moreover, in the present embodiment, the transmission path has been
described as the optical fiber. However, when a transmission
distance is not long, a coaxial cable may be used. In this case,
the electric/optical converter and optical/electric converter are
unnecessary.
Moreover, the electric/optical conversion method of the
electric/optical converter in the control station 2 or the base
station 1 includes a method of directly modulating laser and a
method of using an external optical modulator to perform
modulation. Furthermore, .omega..sub.RF used in ITS or WLL to which
the adaptive antenna is expected to be applied is in a high
frequency band such as 5.8 GHz and 22 GHz.
The band in which direct modulation is possible with a
semiconductor laser is of several GHz at most, and the external
optical modulator is therefore used in the method of directly
converting the high frequency band. However, different from the
electric circuit which can be miniaturized by IC formation even
with the increase of the circuit elements, the optical circuit
cannot be miniaturized. Therefore, the use of the external optical
modulator requires a component space, complicates the constitution,
and raises cost. In the present embodiment, the intermediate
frequency radio signal is subjected to sub-carrier wave
multiplexing and optically transmitted in the constitution, the
laser direct modulation method can be employed, and the optical
transmitter can be simplified in constitution and reduced in
cost.
Eighth Embodiment
In an eighth embodiment, during transmission of an antenna
transmitted signal to the base station from the control station,
the local oscillator output is multiplexed with the antenna
transmitted signal and transmitted.
FIG. 19 is a block diagram of an eighth embodiment of the radio
communication system according to the present invention, and shows
only the constitution of the transmitter for transmitting the
antenna transmitted signal to the base station 1 from the control
station 2.
The control station 2 of FIG. 19 has an IF signal generation
circuit 131 for generating an intermediate frequency signal (IF
signal) for antenna transmission, a distributor 132 for performing
branching to provide the same number of IF signals as the number of
antenna elements, a signal calculation circuit 133 for calculating
a weight coefficient to obtain a desired antenna radiation pattern,
local oscillation circuits 1381 to 138n, couplers 1391 to 139n for
branching the local oscillator output from the local oscillation
circuits, weighting circuits 1341 to 134n for weighting the
respective signals branched by the distributor 132 with the
weighting coefficient; mixers 1351 to 135n for converting the
frequency of the weighted signals by the local oscillator output
branched by the couplers 1391 to 139n, band pass filters 1361 to
136n for extracting only the predetermined frequency component, a
coupler 137 for multiplexing the extracted frequency component and
the other local oscillator output branched by the coupler, and an
optical/electric converter 111 for converting the multiplexed
signal to the optical signal and transmitting the signal to an
optical fiber 112.
The local oscillation circuits 1381 to 138n output the local
oscillator outputs of frequencies f1, f2 to fn, respectively. The
band pass filters 1361 to 136n extract only the signal components
of frequencies (f.sub.1+f.sub.IF), (f.sub.2+f.sub.IF), . . . ,
(f.sub.n+f.sub.IF). Here, f.sub.IF is a frequency of the IF
signal.
The signal multiplexed by the coupler 137 has frequency component
shown by a code 110.
The base station 1 of FIG. 19 has an optical/electric converter 113
for converting the optical signal transmitted from the control
station 2 via the optical fiber to the electric signal; a coupler
114 for branching a part of the electric signal; distributors 115,
116 for distributing the electric signal to provide the same number
of signals as the number of antenna elements, band pass filters
1241 to 124n for extracting only the signal components of
frequencies (f.sub.1+f.sub.IF), (f.sub.2+f.sub.IF), . . . ,
(f.sub.n+f.sub.IF) from outputs of the distributor 115,
respectively, band pass filters 117.sub.1 to 117.sub.n for
extracting only the local oscillator output components from the
outputs of the distributor 116, mixers 118.sub.1 to 118.sub.n for
combining the signals extracted by the band pass filters 124.sub.1
to 124.sub.n, 117.sub.1 to 117.sub.n band pass filters 119.sub.1 to
119.sub.n for extracting only intermediate frequency components
f.sub.IF, mixers 121.sub.1 to 121.sub.n for combining the signals
extracted by the band pass filters 119.sub.1 to 119.sub.n with a
local oscillator output f.sub.RF-IF outputted from a local
oscillation circuit 120, band pass filters 122.sub.1 to 122.sub.n
for extracting only antenna transmitted signal components, and
antennas 4.sub.1 to 4.sub.n.
In the radio communication system of FIG. 19, during generation of
a frequency multiple signal for antenna transmission inside the
control station 2, since the local oscillator output is also
combined, multiplexed, and then transmitted to the base station 1,
the number of local oscillation circuits disposed inside the base
station 1 can be reduced, and the constitution of the base station
1 can be simplified.
Additionally, when the frequencies of the respective signals
inputted to the coupler in the control station 2 are arranged in
order of f.sub.1, (f.sub.1+f.sub.IF), f.sub.2, (f.sub.2+f.sub.IF),
. . . , f.sub.n, (f.sub.n+f.sub.IF) as shown in FIG. 20.
A connection relation of the distributors 115, 116 in the base
station 1 and band pass filters 124.sub.1 to 124.sub.n, 117.sub.1
to 117.sub.n may be set as shown in FIG. 21.
A distributor 201 of FIG. 21 is connected to the band pass filter
124.sub.1 for extracting the signal of frequency
(f.sub.1+f.sub.IF), band pass filter 117.sub.1 for extracting the
signal of frequency f.sub.1, band pass filter 124.sub.2 for
extracting the signal of frequency (f.sub.2+f.sub.IF), band pass
filter 117.sub.2 for extracting the signal of frequency f.sub.2, .
. . , band pass filter 124.sub.n for extracting the signal of
frequency (f.sub.n+f.sub.IF), and band pass filter 117.sub.n for
extracting the signal of frequency f.sub.n.
By the constitution of FIG. 21, the number of distributors can be
reduced as compared with FIG. 19, and no coupler is necessary.
Ninth Embodiment
A ninth embodiment is a modification example of the eighth
embodiment, and a signal obtained by multiplexing the frequency of
RF signal in the control station 2 is transmitted to the base
station 1.
FIG. 22 is a block diagram of the ninth embodiment of the radio
communication system according to the present invention. Since many
parts of the system of FIG. 22 are common to FIG. 19, different
respects will mainly be described hereinafter.
When the bands of the band pass filter, optical/electric converter,
electric/optical converter, and the like are sufficiently obtained,
instead of multiplexing the intermediate frequency signal and
transmitting the signal to the base station 1 from the control
station 2, a radio frequency (RF) signal may be multiplexed and
transmitted.
The control station 2 of FIG. 22 is similar to that of FIG. 19
except that the frequency of antenna transmitted signal is
different, and has RF signal generation circuit 401, distributor
132, signal calculation circuit 133, weighting circuits 404.sub.1
to 404.sub.n, local oscillation circuits 408.sub.1 to 408.sub.n, a
coupler, mixers 405.sub.1 to 405.sub.n, band pass filters 406.sub.1
to 406y, coupler 407, and electric/optical converter 411.
Moreover, the base station 1 of FIG. 22 has an optical/electric
converter 413, distributor 415, band pass filters 424.sub.1 to
424.sub.n and 417.sub.1 to 417.sub.n, mixers 418.sub.1 to
418.sub.n, and band pass filters 419.sub.1 to 419.sub.n.
As shown in FIG. 22, for the base station 1, since a processing of
converting the intermediate frequency signal to the radio signal is
unnecessary, the constitution can further be simplified.
Tenth Embodiment
In a tenth embodiment, contrary to the eighth and ninth
embodiments, when the radio signal received by the base station 1
is converted to the intermediate frequency signal and transmitted
to the control station 2, the intermediate frequency signals and
local oscillator outputs for the number of antenna elements are
multiplexed and transmitted.
FIG. 23 is a block diagram of the tenth embodiment of the radio
communication system according to the present invention. The base
station 1 of FIG. 23 has mixers 503.sub.1 to 503.sub.n for mixing
RF signals received by array antenna elements 501.sub.1 to
501.sub.n with the local oscillator output f.sub.RF-IF from a local
oscillation circuit 502, band pass filters 504.sub.1 to 504.sub.n
for extracting intermediate frequency signals f.sub.IF from output
signals of the mixers 503.sub.1 to 503.sub.n, couplers 507.sub.1 to
507.sub.n for branching the output signals of the band pass filters
504.sub.1 to 504.sub.n and the local oscillator output f.sub.1,
f.sub.2, . . . , f.sub.n, mixers 505.sub.1 to 505.sub.n for mixing
one of the branched local oscillator output with the output signal
of the band pass filter 5041 to 504n, band pass filters 5081 to
508n for extracting different frequency signals (f.sub.1+f.sub.IF),
(f.sub.2+f.sub.IF), . . . , (f.sub.n+f.sub.IF) from output signals
of the mixers 505.sub.1 to 505.sub.n; a coupler 509 for combining
output signals of the band pass filters 508.sub.1 to 508.sub.n with
another local oscillator outputs branched by the coupler, and an
electric/optical converter 510 for converting an output signal of
the coupler 509 to the optical signal.
Moreover, the control station 2 of FIG. 23 has an optical/electric
converter 512 for converting the optical signal transmitted from
the base station 1 via an optical fiber 511 to the electric signal,
distributors 514, 515, band pass filters 520.sub.1 to 520.sub.n for
extracting the signals of the frequencies (f.sub.1+f.sub.IF),
(f.sub.2+f.sub.IF), . . . , (f.sub.n+f.sub.IF), band and pass
filter 516.sub.1 to 516.sub.n for extracting the signal of the
local oscillator output component, mixers 517.sub.1 to 517.sub.n
for combining the respective outputs of the band pass filters
520.sub.1 to 520.sub.n, 516.sub.1 to 516.sub.n, band pass filters
518.sub.1 to 518.sub.n for extracting only IF signals and a beam
forming network 519.
By performing the signal processing of the IF signals outputted
from the band pass filters 518.sub.1 to 518.sub.n by the beam
forming network 519, a desired signal is obtained. In actual, the
amplitude and phase of the IF signal inputted to the beam forming
network 519 are not necessarily the same as the amplitude and phase
received by the antenna because of frequency and phase dispersions
of the respective IF signals outputted from the band pass filters
518.sub.1 to 518.sub.n. However, by performing calibration
beforehand to obtain calibration values in respective branches and
using the calibration values to perform the signal processing in
the beam forming network 519, dispersions of the frequency and
phase can be canceled each other.
As described above, in the radio communication system of FIG. 23,
during frequency multiplexing of the IF signal in the base station
1, since the local oscillator output is also combined, multiplexed
and then transmitted to the control station 2, the number of local
oscillation circuits in the control station 2 can be reduced, and
the constitution of the control station 2 can be simplified.
Eleventh Embodiment
An eleventh embodiment is a combination of the eighth and tenth
embodiments.
FIG. 24 is a block diagram of the eleventh embodiment of the radio
communication system according to the present invention. Respects
different from FIG. 19 and FIG. 23 will mainly be described
hereinafter.
Array antenna constituting elements 624.sub.1 to 624.sub.n are
connected to circulators 623.sub.1 to 623.sub.n for switching
transmission/reception. The local oscillator output outputted from
a local oscillation circuit 620 in the base station 1 is supplied
both to transmitter mixers 621.sub.1 to 621.sub.n and receiver
mixers 625.sub.1 to 625.sub.n. Moreover, local oscillator outputs
f.sub.1 to f.sub.n multiplexed and transmitted to the base station
1 from the control station 2 are supplied not only to transmitter
mixers 618.sub.1 to 618.sub.n but also to receiver mixers 629.sub.1
to 629.sub.n.
As described above, in the radio communication system of FIG. 24,
since the local oscillator output generated in the base station 1
and the local oscillator output multiplexed and transmitted to the
base station 1 from the control station 2 are shared by the
transmission and receiver mixers, the constitutions of the base
station 1 and control station 2 can be simplified.
Twelfth Embodiment
A twelfth embodiment is a modification example of the eleventh
embodiment, and only with respect to the transmitter, the local
oscillator output is multiplexed to the antenna transmitted signal
and transmitted to the base station 1 from the control station
2.
FIG. 25 is a block diagram of the twelfth embodiment of the radio
communication system according to the present invention.
Hereinafter, respects different from FIG. 24 will mainly be
described.
The RF signals received by respective array antenna elements
724.sub.1 to 724.sub.n are converted to IF signals by mixers
725.sub.1 to 725.sub.n and band pass filters 726.sub.1 to 726.sub.n
in the base station 1, and subsequently converted to different
frequency signals by mixers 729.sub.1 to 729.sub.n and band pass
filters 730.sub.1 to 730.sub.n. Output signals of the band pass
filters 730.sub.1 to 730.sub.n are multiplexed by a coupler 740,
converted to a optical signal by an electric/optical converter 741
and transmitted via an optical fiber 742.
The optical signal from the base station 1 is converted to the
electric signal by an optical/electric converter 743 in the control
station 2, and subsequently divided to a plurality of signals by a
distributor 744. Band pass filters 749.sub.1 to 749.sub.n extract
respective signals of frequency components different from the
respective signals divided by the distributor 744.
Mixers 746.sub.1 to 746.sub.n mix the outputs of the band pass
filters 749.sub.1 to 749.sub.n with the local oscillator outputs
from local oscillation circuits 708.sub.1 to 708.sub.n used in
common to the transmitter. Band pass filters 747.sub.1 to 747.sub.n
extract only the IF signals from the outputs of the mixers
746.sub.1 to 746.sub.n, and a beam forming network 748 performs a
signal processing based on the IF signals.
As described above, in the twelfth embodiment, with respect to the
receiver, since the multiplexing of the received signal and local
oscillator output is not performed, the processing of extracting
the local oscillator output on the control station 2 side is
unnecessary, and the constitution of the control station 2 can be
simplified.
Additionally, in the radio communication system of FIG. 25, the
antenna received signal transmitted to the control station 2 from
the base station 1 is converted to the IF signal using the local
oscillator output utilized in the transmitter, deviations of the
frequency and phase possibly occur. The deviations need to be
corrected in the beam forming network 748. Specifically,
calibration is performed beforehand to obtain the calibration value
in each branch, and the correction processing may be performed in
the beam forming network based on the calibration value.
Thirteenth Embodiment
In a thirteenth embodiment, the arrival direction of a radio wave
can be estimated without taking synchronization of a frequency
converter in the base station with the frequency converter in the
control station.
FIG. 26 is a block diagram schematically showing a constitution of
the radio communication system according to the present invention.
The base station 1 of FIG. 26, as the receiver constitution, has
the array antenna 4 constituted of n element antennas 4a to 4n for
performing transmission/reception of radio signals with a radio
communication terminal (not shown) so that directivity of a
transmission/reception beam can be changed; a beam forming network
121 for combining the signals received by the respective element
antennas 4a to 4n and converting the signal to m beam components,
circulators 36a to 36m for separating the transmitted/received
signal, m pieces of frequency converters (D/C: first frequency
conversion means) 201a to 201m for converting the output signals of
the beam forming network 121 to respective different frequencies,
the combiner (MUX: first frequency multiplexing means) 9 for
combining the output signals from the m frequency converters 201a
to 201m and performing frequency multiplexing, and the
electric/optical converter (E/O: first electric/optical conversion
means) 10 for converting the output signals of the combiner 9 to
the optical signal.
Moreover, the base station 1 of FIG. 26, as the transmitter
constitution, has the optical/electric converter (O/E: first
optical/electric conversion means) 31 for converting the optical
signal transmitted from the control station 2 to the electric
signal as described later, a separation circuit (DIV: separation
means) 122 for dividing the output signal of the optical/electric
converter 31 to the transmitted signal for the radio communication
terminal and the signal for controlling the radiation beam-pattern
of the array antenna 4, a frequency converter (U/C: second
frequency conversion means) 202 for converting the frequency of the
transmitted signal for the radio communication terminal separated
by the separation circuit 122 to the radio frequency, a
transmission beam control circuit 123 for generating a transmission
beam control signal based on the signal separated by the separation
circuit 122 for controlling the radiation beam-pattern of the array
antenna 4, and the divider (antenna control means) 32 for dividing
the output signal of the frequency converter 202 to a plurality of
signals in accordance with the radiation beam-pattern of the
respective element antennas 4a to 4n based on the transmission beam
control signal. The signals divided by the divider 32 are inputted
to the beam forming network 121 via the circulators 36a to 36m, and
supplied to the element antennas 4a to 4n so that the signal is
radiated as the beam provided with a predetermined directivity.
On the other hand, the control station 2 of FIG. 26, as the
receiver constitution, has the optical/electric converter (O/E:
second optical/electric conversion means) 11 for converting the
optical signal transmitted from the base station 1 via the optical
fiber 3 to the electric signal, a divider or demultiplexer
(demultiplex means) 12 for dividing the converted electric signal
to m frequency signals before frequency multiplexing, m pieces of
frequency converters (D/C: third frequency conversion means) 203a
to 203m for converting the frequencies of the respective signals
divided by the divider 12 to the predetermined same frequency,
weighting circuits (W: weighting means) 17a to 17m for weighting
the output signals of the frequency converters 203a to 203m with
respect to phase and signal intensity, a combiner 18 for combining
the respective weighted signals and a demodulator (DEM:
demodulation means) 19 for demodulating the synthesized signal to
obtain transmission information from a mobile unit.
Moreover, the control station 2 of FIG. 26, as the transmitter
constitution, has a level detector (level detection means) 124 for
detecting a highest level signal among the output signals of the m
frequency converters 203a to 203m or a signal intensity
distribution to output a transmission beam control signal, a
modulator (MOD) 41 for outputting a transmission base band signal a
frequency converter (U/C) 204 for converting the frequency of the
base band signal; combiner 46 for multiplexing the output signal of
the frequency converter 204 with the transmission beam control
signal from the level detector 124, and electric/optical converter
(E/O: second electric/optical conversion means) 47 for converting
the signal multiplexed by the combiner 46 to the optical signal and
transmitting the optical signal to the base station 1 via the
optical fiber 3.
An operation of the radio communication system of FIG. 26 will next
be described. The radio frequency signal from the radio
communication terminal (not shown) is received by the array antenna
4, and subsequently converted to beam components whose peak
directions are different from one another by the beam forming
network 121. The output signals of the beam forming network 121 are
converted to frequencies different from each other, respectively
and subjected to frequency multiplexing by the combiner 9. The
output signal of the combiner 9 is converted to the optical signal
from the electric signal by the electric/optical converter 10, and
subsequently transmitted to the control station 2 via the optical
fiber 3.
The optical signal transmitted to the control station 2 from the
base station 1 is converted to the electric signal by the
optical/electric converter 11, divided to m pieces of signals by
the divider 12, inputted to the corresponding frequency converters
203a to 203m and converted to the same frequency. The output
signals of the frequency converters 203a to 203m are weighted
optimally, and then combined by the combiner 18, and subsequently
demodulated by the demodulator 19.
Here, since the frequency converters 201a to 201m in the base
station 1 are not synchronized with the frequency converters 203a
to 203m in the control station 2, the phase relation among the
respective beams formed in the beam forming network 121 in the base
station 1 is not held in the control station 2. Therefore, it is
difficult to estimate the arrival direction of the received signal
from the weight added by the weighting circuits 17a to 17m.
However, when the respective beams formed by the beam forming
network 121 are different, for example, in main beam from one
another, and the whole main beam can cover an illuminating area of
the base station 1, it is possible to estimate the received signal
arrival direction by the amplitude value of each beam.
Specifically, the beams formed by the beam forming network 121 have
maximum directivity in respective different directions, and a
plurality of beams cover the communication range of the base
station 1. Therefore, for any one of the plurality of beams, a
mobile station terminal to be communicated exists in a beam
width.
Generally, since the beam is formed so that a gain is lowered in
the vicinity of a beam maximum radiation direction of another beam,
it can be considered that the mobile station terminal exists in the
direction of the beam received with a highest electric field
intensity.
Therefore, the level detector 124 compares the signal amplitudes of
the respective outputs of the frequency converters 203a to 203m
with one another, and determines a highest level signal as the
transmission beam. The transmission beam control signal outputted
from the level detector 124 includes, for example, information
corresponding to beam numbers of the beam forming network 121.
FIG. 27 is diagram showing properties of the beam formed by the
beam forming network 121. Supposing that the irradiation area of
the base station 1 has an angle of .theta.1 to .theta.2, and the
area is covered with m beams, the beam forming network 121 combines
the received signals in the antenna elements 4a to 4n so that each
of the m beams has a beam width of |.theta.1 .theta.2| /m[.degree.]
as shown in FIG. 27A. These received signals are outputted from
different output terminals of the beam forming network 121.
Therefore, m output terminals of the beam forming network 121 has a
one-to-one correspondence with m beams of FIG. 27A.
For example, supposing that a radio wave is incident from a
.theta.i direction, the power in each output terminal of the beam
forming network 121 is as shown in FIG. 27B. As shown in the
drawings, the reception power in beam i with the .theta.i direction
in a main beam is largest, and beams (i+1), (i-1) have the .theta.i
direction in the vicinity of the main beam, and therefore have
certain degrees of reception powers although they are lower than
the reception power of the beam i. On the other hand, for the other
beams, since .theta.i exists in a side lobe area, the reception
power is lowered.
Therefore, the arrival direction of the radio wave can be estimated
to some degree by the beam having the maximum reception power
(maximum signal intensity) and a reception power distribution
(signal intensity distribution) of the respective beams. Moreover,
in this case, when the beam i is selected as the transmission beam
on the base station 1 side, power can efficiently be supplied to
the mobile station terminal as a communication destination, and a
mobile station terminal sensitivity is enhanced, or there is
another merit that noises to the other terminals can be
reduced.
On the other hand, a flow of transmitted signal in the system of
FIG. 26 is as follows. An output base band signal from the
modulator 41 is converted up in the frequency converter 204,
frequency-multiplexed with the transmission beam control signal as
the output signal of the level detector 124, optically modulated
and transmitted to the base station 1.
After the optical signal transmitted to the base station 1 is
converted to the electric signal by the optical/electric converter
31, and subsequently divided to the antenna transmitted signal and
transmission beam control signal by the separation circuit 122.
The antenna transmitted signal separated by the separation circuit
122 is converted up by the frequency converter 202. Moreover, the
transmission beam control signal separated by the separation
circuit 122 is inputted to the divider 32 via the transmission beam
control circuit 123.
The divider 32 divides the output signal of the frequency converter
202. The divider 32 adjusts the signal intensity of the output
signal of the frequency converter based on the output signal of the
transmission beam control circuit 123, and outputs the signal to
the element antennas 4a to 4n. That is, the divider 32 supplies all
the signals to one terminal as a switch, or distributes to some
beam terminals at an appropriate distribution ratio based on the
output signal of the transmission beam control circuit 123.
The output signal of the divider 32 is inputted to the beam forming
network 121 via the circulators 36a to 36m, and the beam signals to
the respective element antennas 4a to 4n are formed.
As described above, in the first embodiment, since the intensity
maximum value or the intensity distribution of the converted
signals is detected in a beam space by the level detector 124 to
determine the radiation directivity during transmission, the radio
wave arrival direction can be estimated without synchronizing the
frequency converters 201a to 201m in the base station 1 with the
frequency converters 203a to 203m in the control station 2.
Therefore, the synchronization among the frequency converters 201a
to 201m, and the frequency converters 203a to 203m in the control
station 2 is unnecessary, and the constitution of the control
station 2 can be simplified.
Moreover, in the thirteenth embodiment, the beam control signal for
transmission control is multiplexed with the modulation signal for
transmission (antenna transmitted signal) in the control station 2
and transmitted to the base station 1 so that the transmitted
signal is radiated in the radio wave arrival direction estimated
based on the received signal, beam formation is performed in the
base station 1, it is therefore unnecessary to form and multiplex
the beams for the respective element antennas 4a to 4n in the
control station 2, and the transmitter constitution can be
simplified.
Fourteenth Embodiment
In a fourteenth embodiment, by using the antenna provided with a
directional pattern, the beam forming network 121 is omitted and
the constitution of the base station 1 is simplified.
FIG. 28 is a block diagram of a fourteenth embodiment of the radio
communication system according to the present invention. In FIG.
28, the constituting parts common to those of FIG. 26 are denoted
with the same reference numerals, and different respects will
mainly be described hereinafter.
The base station 1 of FIG. 28 is constituted similarly as the base
station 1 of FIG. 26, except that a plurality of directional
antennas 4a to 4n provided with desired directional patterns
different from one another, for example, like a sector antenna are
disposed, and the beam forming network 121 of FIG. 26 is omitted.
Moreover, the control station 2 of FIG. 28 is constituted similarly
as the control station 2 of FIG. 26.
Since the plurality of antennas 4a to 4n of FIG. 28 are different
in directivity from one another, by detecting the maximum intensity
and intensity distribution of the signals received by the
respective antennas 4a to 4n by the level detector 124 in the
control station 2, the radio wave arrival direction can correctly
be estimated. Therefore, the beam forming network 121 of FIG. 26 is
unnecessary, the constitution of the base station 1 can further be
simplified, and miniaturization and cost reduction are
possible.
FIG. 29A is a diagram schematically showing beam forming in the
directional antennas 4a to 4n of FIG. 26, and FIG. 29B is a diagram
schematically showing beam formation by the element antennas 4a to
4n and beam forming network 121 of FIG. 26.
As shown in FIG. 29B, the beam forming network 121 of FIG. 26
multiplies the signal by a certain composite weight for each of the
element antennas 4a to 4n, synthesizes the signal and forms a
desired directional pattern, depending on input ports of the
inputted signal.
On the other hand, when the directional antennas 4a to 4n as shown
in FIG. 28 (e.g., a reflective mirror antenna, a sector beam
antenna, and the like) are used, as shown in FIG. 29A, antenna
units are different in maximum radiation direction from one
another, and have desired directional patterns such as a
predetermined beam width and gain. Therefore, the properties equal
to those of the first embodiment of the present invention can be
obtained without combining the received signals of the respective
element antennas 4a to 4n as shown in FIG. 29B.
Therefore, in the fourteenth embodiment of the present invention,
it is possible to estimate the radio wave arrival direction from
the individual received signal intensities without the beam forming
network 121.
Fourteenth Embodiment
In the thirteenth and fourteenth embodiments, the signal received
by the antenna is weighted and demodulated in an analog signal
state, but in a fifteenth embodiment the signal is converted to a
digital signal, weighted in a digital manner and subsequently
demodulated.
FIG. 30 is a block diagram of the fifteenth embodiment of the radio
communication system according to the present invention. In FIG.
30, the constituting part common to FIG. 26 is denoted with the
same reference numerals, and different respects will mainly be
described hereinafter.
The base station 1 of FIG. 30 is constituted similarly as the base
station 1 of FIG. 26. The control station 2 of FIG. 30 has m
analog/digital converters (A/D conversion means) 125a to 125m for
converting the received signals converted to the same frequency by
the frequency converters 203a to 203m to digital signals, and a
digital signal processor (digital signal processing means) 126 for
subjecting the digital signals to predetermined weighting and
synthesis in a digital manner and subsequently performing
demodulation.
In the system of FIG. 30, since it is unnecessary to perform analog
weighting, integration is facilitated as compared with the first
embodiment, and the control station 2 can be miniaturized.
Moreover, in the digital signal processor 126, not only phase
adjustment but also further complicated/sophisticated controls of
the base station 1 such as interference suppression, arrival
direction estimation, and delay wave synthesis are possible by
changing a digital signal processing algorithm without adding any
hardware.
Moreover, in FIG. 30, the output signals of the frequency
converters 203a to 203m are inputted to the level detector 124, but
the signal resulting from the signal processing by the digital
signal processing circuit 126 may be inputted to the level detector
124 to generate a control signal for directivity control.
The level detector 124 of the aforementioned fourteenth and
fifteenth embodiments generates the control signal for the
radiation beam-pattern control based on the intensity of the
received signal transmitted to the control station 2 from the base
station 1. However, when the position information of the radio
communication terminal is known on a network side, by inputting the
position information to the level detector 124, the control signal
for the radiation beam-pattern control may be outputted based on
the position information and received signal intensity.
Sixteenth Embodiment
In a sixteenth embodiment, the level detector 124 is disposed in
the base station 1, and the control signal for the radiation
beam-pattern control is generated in the base station 1.
FIG. 31 is a block diagram of the sixteenth embodiment of the radio
communication system according to the present invention. In FIG.
31, the constituting part common to FIG. 26 is denoted with the
same reference numerals, and different respects will mainly be
described hereinafter.
In addition to the constitution of FIG. 26, the base station 1 of
FIG. 31 has the level detector 124 for detecting the maximum
intensity and intensity distribution of the output signals of the
frequency converters 201a to 201m to generate the control signal
for the radiation beam-pattern control. The transmission beam
control circuit 123 in the base station 1 generates the beam
control signal for antenna transmission based on the control signal
from the level detector 124.
On the other hand, the control station 2 of FIG. 31 is constituted
by removing the level detector 124 and combiner 46 from the
constitution of FIG. 26.
In the system of FIG. 31, since the received signal level detection
and transmitting radiation pattern control are performed in the
base station 1, it is unnecessary to dispose the level detector 124
and combiner 46 in the control station 2, and the constitution of
the control station 2 can be simplified.
Moreover, during transmission of the antenna transmitted signal to
the base station 1 from the control station 2, since it is
unnecessary to multiplex the transmitted signal with the
transmitting radiation pattern control signal in the control
station 2, the constitution of the transmitter to the base station
1 from the control station 2 can be simplified.
Seventeenth Embodiment
A seventeenth embodiment is a modification example of the sixteenth
embodiment, and during transmission of the received signal to the
control station 2 from the base station 1, instead of transmitting
all the beams formed by the beam forming network 121, only the beam
with a high signal level is selected and transmitted.
FIG. 32 is a block diagram of the seventeenth embodiment of the
radio communication system according to the present invention. In
FIG. 32, the constituting part common to FIG. 26 is denoted with
the same reference numerals, and different respects will mainly be
described hereinafter.
In addition to the constitution of FIG. 26, the base station 1 of
FIG. 32 has a reception beam selection circuit (received signal
selection means) 127 for selecting only some of output signals of
the frequency converters 201a to 201m based on the beam control
signal outputted from the level detector 124. Concretely, the
reception beam selection circuit 127 mainly selects some signals
with high signal intensities from the signals subjected to the
frequency conversion by the frequency converters 201a to 201m. The
combiner 9 multiplexes only the signals selected by the reception
beam selection circuit 127. The multiplexed signal is converted to
the optical signal by the electric/optical converter 31 and
transmitted to the control station 2.
The control station 2 of FIG. 32 is constituted similarly as FIG.
26. However, since the number of signals transmitted from the base
station 1 decreases, a weighting processing of the respective
signals, a synthesis processing of the respective weighted signals,
and the like become easier than those of FIG. 26, and the
constitution of the control station 2 can be simplified.
For example, FIG. 33 shows an example in which the directional
antenna 4a' to 4n' are connected instead of the array antenna 4 in
the circuit of FIG. 31.
In FIGS. 26, 28, 31, 32 and 33, the respective beams in the control
station 2 are weighted in an analog manner as described above, but
similarly as FIG. 30, by disposing an A/D converter and digital
signal processing circuit in the control station 2, and converting
the received signal to the digital signal by the A/D converter, the
weighting processing, synthesis processing, demodulation
processing, and the like may be performed in a digital manner in
the digital signal processing circuit.
Similarly as FIG. 28, the directional antenna may be used instead
of the array antenna 4, and this obviates the necessity of the beam
forming network 121. For example, FIG. 33 shows an example in which
the directional antennas 4a to 4n are connected instead of the
array antenna 4 in the circuit of FIG. 31. FIGS. 31 to 33 show an
example in which the beam forming network 121 is disposed similarly
as FIG. 26.
Moreover, in the fourteenth to seventeenth embodiments, an example
has been described in which the array antenna 4 is shared for
transmission/reception, and the circulators 36a to 36m are
connected to the ends of the element antennas 4a to 4n, but the
beam forming network 121 is also shared for transmission/reception.
However, by separately disposing the transmitting antenna and the
receiving antenna, the beam forming network 121 may also be
disposed separately for transmission and reception. In this case,
no transmission/reception separation circuit is necessary.
Furthermore, in the aforementioned fourteenth to seventeenth
embodiments, the radio frequency signals received by the respective
element antennas 4a to 4n are once converted to the intermediate
frequency signals, optically modulated and subsequently transmitted
to the control station 2. A reason for this is that the
electric/optical converter 31 and optical/electric converter 11 can
be realized more inexpensively than when the optical modulation is
performed with the radio frequency signal. Additionally, the radio
frequency signal may optically be modulated and transmitted to the
control station 2. Also in this case, it is possible to use the
level detector 124 and estimate the radio wave arrival
direction.
Moreover, also in the system of FIG. 26 or 29, similarly as FIG.
32, by disposing the reception beam selection circuit 127 in the
base station 1, only some of the received signals may be selected,
subjected to frequency multiplexing and transmitted to the control
station 2.
Eighteenth Embodiment
In an eighteenth embodiment, the phase and amplitude adjustment of
the transmitted signal transmitted to the base station from the
control station is easily and precisely performed.
FIG. 34 is a block diagram of the eighteenth embodiment of the
radio communication system according to the present invention. A
system of FIG. 34 shows an example in which the base station 1
provided with the array antenna 4 is connected to the control
station 2 via the optical fiber 3, and sub-carrier multiplexing
transmission is performed. The array antenna 4 of FIG. 34 includes
three antenna elements 4a to 4c, but the number of antenna elements
4a to 4c is not particularly limited.
The base station 1 of FIG. 34, as the receiver configuration, has
circulators 36a to 36c for switching transmission/reception,
combiners (combiner means) 162a to 162c for performing synthesis of
transmitted/received signals, a pilot signal inserter (pilot signal
insertion means) 160 for inserting a pilot signal into a
transmitted signal fed back to the control station 2, low noise
amplifiers 5a to 5c for amplifying the output signal of the pilot
signal inserter 160, frequency converters (first frequency
conversion means) 201a to 201c for down-converting the respective
output signals of the low noise amplifiers 5a to 5c to different
frequency signals, combiner (frequency multiplexing means) 9 for
performing sub-carrier multiplexing for the respective frequency
signals outputted from the frequency converters 201a to 201c, and
electric/optical converter (first electric/optical conversion
means) 10 for converting the signal synthesized by the combiner 9
to the optical signal and transmitting the optical signal to the
control station 2 via the optical fiber 3.
Moreover, at the transmitter side, the base station 1 of FIG. 34
has optical/electric converter 31 for converting the optical signal
transmitted from the control station 2 to the electric signal,
divider 32 for dividing the output signal of the optical/electric
converter 31 to plural signals with different frequency, frequency
converters 202a to 202c for converting the respective frequency
signals divided by the divider 32 to radio frequency signals,
amplifiers 35a to 35c for amplifying the output signals of the
frequency converters 202a to 202c, and couplers 161a to 161c for
branching the output signals of the amplifiers 35a to 35c to the
circulators 36a to 36c and combiners 162a to 162c.
Additionally, the base station 1 of FIG. 34 has a frequency
synthesizer 16 for supplying local oscillator outputs to the
frequency converters 201a to 201c, 202a to 202c. The frequency
synthesizer 16 has plural local oscillators for generating
different frequency signals, or has one local oscillator and a
frequency divider for multiplying or dividing the frequency of the
local oscillation signal to generate various frequency signals.
On the other hand, at the receiver side, the control station 2 of
FIG. 34 has the optical/electric converter (optical/electric
conversion means) 11 for converting the optical signal transmitted
from the base station 1 to the electric signal, distributor
(demultiplex means) 12 for dividing the output signal of the
optical/electric converter 11 to plural sub-carrier signals,
frequency converters (third frequency conversion means) 14a to 14c
for converting the respective distributor outputs to the same
frequency, feedback signal detector (feedback means) 163 for
detecting transmitted feedback signal from the output signals of
the frequency converters 14a to 14c, calibration coefficient
calculation circuit (comparison means) 164 for calculating the
calibration coefficient for transmission by using the feedback
signal, adaptive antenna weighting coefficient calculation circuit
(weighting coefficient calculation means) 165 for calculating the
weighting coefficients for transmission/reception taking the
calibration coefficient, multipliers (first weighting means) 17a to
17c for weighting the received signal based on the calculated
weighting coefficient, combiner 18 for synthesizing the respective
output signals of the multipliers 17a to 17c, and demodulator 19
for demodulating the signal synthesized by the combiner 18.
Moreover, the control station 2, as the transmitter constitution,
has the modulator 41 for generating the modulation signal for
transmission, distributor 42 for dividing the modulation signal to
a plurality of signals, multipliers (second weighting means) 43a to
43c for weighting the divided modulation signals based on the
weighting coefficient, frequency converters 204a to 204c for
converting the output signals of the multipliers 43a to 43c to
different frequency signals, combiner 46 for performing sub-carrier
multiplex for the output signals of the frequency converters 204a
to 204c, and electric/optical converter 47 for converting the
signal multiplexed by the combiner 46 to the optical signal and
transmitting the optical signal to the base station 1 via the
optical fiber 3.
Additionally, the control station 2 of FIG. 34 has frequency
synthesizer 13 for supplying local oscillator outputs to the
frequency converters 14a to 14c, 204a to 204c, respectively. The
frequency synthesizer 13 has plural local oscillators for
generating different frequency signals, or has one local
oscillator, and a frequency divider for multiplying or dividing the
local oscillator output to generate various frequency signals. In
the present embodiment, it is supposed that the frequency
synthesizer 16 in the base station 1 is synchronized in frequency
and phase with the frequency synthesizer 13 in the control station
2.
In the base station 1 of FIG. 34, the couplers 161a to 161c, the
combiners 162a to 162c, pilot signal inserter 160 correspond to
feedback means, and the frequency converters 201a to 201c, combiner
9, and electric/optical converter 10 correspond to transmission
means. Moreover, in the control station 2 of FIG. 34, the weighting
coefficient calculation circuit 165 and multipliers 17a to 17c, 43a
to 43c correspond to compensation means, and the feedback signal
detector 163 corresponds to first and second detection means.
The base station 1 of FIG. 34 returns the transmitted signals from
the control station 2 back to the control station 2 via the
receiver circuits in the base station 1 before radiation from the
array antenna 4. Moreover, the control station 2 compares two
signals among the transmitted signals of the respective branches
fedback with the inserted pilot signals. In this case, since an
absolute phase and an absolute amplitude of the pilot signal are
known in the control station 2 in advance, the pilot signal are
used to estimate phase/amplitude fluctuation amount of each branch
in the receiver from the base station to the control station. It is
also possible to perform adjustment of each branch of the
transmitter, by subtracting the phase/amplitude fluctuation amount
of the receiver estimated by the pilot signal.
An operation of the radio communication system of FIG. 34 will be
described hereinafter. The signals received by the antenna elements
4a to 4c and the transmitted signal from the control station 2 are
combined by the combiners 162a to 162c, and provided with the pilot
signal by the pilot signal inserter 160. Thereafter, the signals
are inputted to the frequency converters 201a to 201c via the low
noise amplifiers 5a to 5c, and converted to different frequencies
for the respective branches corresponding to the respective antenna
elements 4a to 4c. In this case, the frequency is preferably
converted to an intermediate frequency in accordance with the
frequency properties, and the like of the optical fiber 3 and
optical source. By the conversion to the intermediate frequency,
the constitution of the optical transmitter can be simplified. The
output signals of the frequency converters 201a to 201c are
subjected to frequency multiplexing by the combiner 9, converted to
the optical signal by the electric/optical converter 10 and
transmitted to the control station 1.
FIG. 35 is a frequency spectrum diagram of the signal subjected to
sub-carrier frequency multiplexing by the combiner 9. FIG. 35 shows
an example of a frequency divide duplex (FDD) system that
transmitted/received signals are assigned to the frequencies
different from each other. As shown in FIG. 35, the received signal
in the array antenna 4, pilot signal, and transmitted signal from
the control station 2 are assigned at different frequency
intervals, and these are assigned as a group to sub-carriers f1 to
f3. Additionally, band-pass filters (not shown) in the frequency
converters 201a to 201c need to be provided with bandwidth in which
the signal groups of the respective sub-carriers can pass.
Furthermore, when the pilot signal is subjected to frequency
multiplexing and inserted, it is necessary to allocate the neighbor
frequency band to the pilot signal so closely that phase/amplitude
fluctuation amount due to difference of the frequency property does
not change.
The optical signal transmitted to the control station 2 is again
converted to the electric signal by optical/electric converter 11,
and subsequently divided to a plurality of branch signals by the
divider 12. These branch signals are converted to the same
frequency signals by the frequency converters 14a to 14c, and
inputted to the feedback signal detector 163 and multipliers 17a to
17c.
The feedback signal detector 163 extracts the transmitted signals
transmitted by the control station 2, and pilot signal.
The calibration coefficient calculation circuit 164 uses the
transmitted signal of either one of the branches as a reference
among the respective branch transmitted signals extracted by the
feedback signal detector 163, and detects the relative phase
difference and relative amplitude difference in the other branches.
Based on the detected result, the circuit 164 detects consistent
signal distortion in the transmitter/receivers. Furthermore, the
circuit 164 detects calibration coefficients of each branch of the
transmitter by subtracting phase/amplitude fluctuation amount of
the receiver estimated from the distortion of the pilot signal.
The weighting coefficient calculation circuit 165 calculates the
weighting coefficients with respect to the transmission and
received signals by using the output signals of the frequency
converters 14a to 14c, the calibration coefficients calculated by
the calibration coefficient calculation circuit 164, and the
transmission/reception weight calculated for beam control.
The multipliers 17a to 17c multiply the output signals of the
frequency converters 14a to 14c by the weighting coefficient
calculated at the weighting coefficient calculation circuit 165 to
perform weighting of the received signal. The weighted received
signal is inputted to the demodulator 19 and demodulated.
On the other hand, the transmitted signal modulated by the
modulator 41 in the control station 2 is multiplied by the
weighting coefficient calculated by the weighting coefficient
calculation circuit 165 by the multipliers 43a to 43c, and
weighted. The weighted transmitted signals are converted to
different frequency signals by the frequency converters 204a to
204c, and subsequently subjected to sub-carrier frequency
multiplexing by the combiner 46.
The transmitted signal subjected to the sub-carrier frequency
multiplexing is converted to the optical signal by the
electric/optical converter 47, and subsequently transmitted to the
base station 1 via the optical fiber 3.
The optical signal transmitted to the base station 1 is divided to
a plurality of branch signals by the divider 32, and the respective
branch signals are inputted to the frequency converters 202a to
202c and converted up to the radio frequency signal.
The respective output signals of the frequency converters 202a to
202c are inputted to the amplifiers 35a to 35c, amplified and
subsequently inputted to the antenna elements 4a to 4c via the
couplers 161a to 161c and circulators 36a to 36c.
The detailed constitution and operation of the feedback signal
detector 163, calibration coefficient calculation circuit 164, and
weighting coefficient calculation circuit 165 of FIG. 34 will next
be described.
The feedback signal detector 163 extracts the transmitted signal of
each branch and the pilot signal from the sub-carrier shown in FIG.
36. When the pilot signal is subjected to frequency multiplexing
with the fedback transmitted signal, a specific narrow band-pass
filter is necessary.
As shown in detail in FIG. 36, the calibration coefficient
calculation circuit 164 has a phase difference detector 166,
amplitude ratio detector 167, and calculator 168.
Any two branches of signals among the respective output signals of
the frequency converters 14a to 14c are inputted to both the phase
difference detector 166 and the amplitude ratio detector 167. The
phase difference detector 166 detects a phase difference between
the output signals, and the amplitude ratio detector 167 detects an
amplitude deviation between the output signals.
Especially, when detecting the relative phase difference/amplitude
fluctuation amount of each branch, for example, the feedback signal
of the first branch is always inputted from the input part 1, and
another feedback signals are inputted from the input part 2.
When a first branch is used as a reference, the relative phase
difference of a k-th branch is .theta.1k, and the relative
amplitude ratio is Alk, the calculator 168 calculates calibration
coefficients C1 to C3 based on the following equations (23) to
(25). C.sub.1=1 (23)
.times.e.theta. ##EQU00015##
.times.e.theta. ##EQU00016##
As shown in detail in FIG. 37, the phase difference detector 166 of
FIG. 36 has a multiplier 169, low pass filter 170, and phase
identifier 171. After the feedback signals of i number branch and j
number branch is multiplied by the multiplier 169, high frequency
components are removed by the low pass filter 170, so that
deviation components can be obtained in proportion to
cos.theta.ij.
As shown in detail in FIG. 38, the amplitude ratio detector 167 of
FIG. 36 has a phase compensator 172, diodes 173a, 173b, sampling
units 174a, 174b, and divider 175. The phase compensator 172
corrects the phase difference of one of the inputted two
transmitted signals to input the same phase. The output of the
phase compensator 172 and the other feedback signal are inputted to
the diodes 173a, 173b, respectively, and envelope components are
extracted. These envelope components are sampled by the sampling
units 174a, 174b, and a sampling output ratio is obtained by the
divider 175,
By performing the same process relating to the pilot signal, it is
possible to estimate the absolute phase fluctuation amount .phi.k
and the absolute amplitude fluctuation amount Bk of each branch of
the receiver. In this case, known sequence of the pilot signal is
inputted to the input port 1 of the calibration coefficient
calculation circuit of FIG. 37, and the fedback pilot signal is
inputted to the input port 2. Therefore, the relative phase
fluctuation amount of only the transmitter is given by
.theta.'1k=.theta.1k-.phi.k. The relative amplitude fluctuation
amount of only the transmitter is given by A'1k=A1k/B1k.
Therefore, calibration coefficient CT of the transmitter to be
compensated is as in equations (26) to (28). C.sub.T1=1 (26)
'.times.e.theta.' ##EQU00017##
'.times.e.theta.' ##EQU00018##
The weighting coefficient calculation circuit 165 calculates the
weighting coefficients w'T1 to w'T3 including the calibration value
of the transmitter by using the relative output signals of the
calibration coefficients obtained by the calibration coefficient
calculation circuit 164 and the relative output signals of the
frequency converters 14a to 14c. When the transmission weight to
form a desired antenna pattern is WT1 to WT3, by the equations (26)
to (28), the transmission weighting coefficient including the
calibration value weighted by the multipliers 43a to 43c, the
weighting coefficient is obtained by equation (29). wTk=w'TkCTk
(k=1,2,3) (29)
By weighting as shown in the aforementioned equations (26) to (29),
a desired transmitting beam pattern is obtained at an antenna
end.
Similarly, calibration coefficient CRi of the receiver is
represented by the following equations (30) to (32).
.times.e.PHI. ##EQU00019##
.times.e.PHI. ##EQU00020##
.times.e.PHI. ##EQU00021##
The calibration coefficient calculation circuit 164 of FIG. 34
calculates the transmitter calibration coefficient based on the
aforementioned equations (26) to (29), and calculates the receiver
calibration coefficient based on the aforementioned equations (30)
to (32). Moreover, the weighting coefficient calculation circuit
165 calculates the weighting coefficient with respect to the
transmitted signal based on the aforementioned equation (29), and
similarly calculates the weighting coefficient with respect to the
received signal.
The pilot signal inserted by the pilot signal inserter 160 will
next be described. The pilot signal consists, for example, of PN
(pseudo random noise) sequence, and its sequence pattern is known
between the control station 2 and the base station 1. Moreover, the
pilot signal can be inserted by time division multiplex, besides
being inserted to the fedback transmitted signal by the frequency
division multiplex. In this case, because the pilot signal and the
feedback signal pass the receiver having the same frequency
property, it is possible to more precisely detect distortion of the
receiver. Even in either case, it is necessary to insert the pilot
signal with equal amplitude simultaneously at each branch
When the PN sequence is simultaneously inserted as the pilot
signal, by performing a correlation processing of PN sequence
length, a strongly impulsive correlation output which indicates
delay timing and correlation strength is obtained from the pilot
signal of each branch introduced by the feedback signal detector
163, as shown in FIG. 39. By the correlation output, reaching delay
time differences t1, t2 among the branches in the receiver can be
observed, and fluctuation phase difference .phi.k can be estimated.
Moreover, by detecting peak values, relative amplitude ratio Bk
among the branches of the receiver can be estimated.
In the aforementioned embodiment, the pilot signal of the PN
sequence is used, but only a sinusoidal carrier wave may be fed
back as the pilot signal. In this case, the feedback signal
detector 163 of the control station 2 can estimate a relative phase
fluctuation amount .phi.k and relative amplitude fluctuation amount
Bk by the multiplier and low pass filter similarly as the
aforementioned constitution of the phase difference detector.
In this manner, in the eighteenth embodiment, since the feedback
signal of the transmitted signal, the received signal in the array
antenna 4, and the pilot signal are multiplexed and transmitted to
the control station 2 from the base station 1, the relative phase
difference and relative amplitude fluctuation amount can be
detected by using the pilot signal in the control station 2.
Moreover, the use of the pilot signal can establish synchronization
of the respective local oscillator outputs from the frequency
synthesizers 16 and 13, and synchronization of the respective
branch signals transmitted between the base station 1 and the
control station 2.
Moreover, in the eighteenth embodiment, since the relative phase
difference and relative amplitude fluctuation amount can be
detected using the phase difference detector 166 and amplitude
ratio detector 167 simply constituted as shown in FIGS. 38 and 39,
the system constitution can be simplified, and it is possible to
reduce cost. Moreover, transmission beam control can precisely be
performed in the adaptive antenna, moving of a terminal station can
be followed by a high gain and narrow beam, the coverage by one
base station 1 can be enlarged, and the probability of loss by busy
channel of hand-off destination base station 1 can be
minimized.
Furthermore, since null control which is more sensitive angularly
than main beam control can precisely be controlled, interference
with the terminal station in communication with the adjacent base
station 1 or another base station 1 can be suppressed,
communication quality can be improved, and the entire system
capacity can be enhanced.
Additionally, in the aforementioned eighteenth embodiment, as shown
in FIG. 35, the method of subjecting the transmitted signal and
pilot signal to frequency multiplexing has been described, but a
method of multiplexing the transmitted signal and pilot signal in
time division for feedback to the control station 2 may be
employed.
By employing this method, the pass band width of the frequency
converter can be narrowed, and estimation error by the slight
influence of frequency properties of the respective components can
be prevented from occurring.
Moreover, since it is easy to separate the multiplexed received
signal, transmitted signal and pilot signal after reception,
calibration can be performed even during communication, and no
disadvantage of interruption of communication by calibration
occurs.
Nineteenth Embodiment
In a nineteenth embodiment, the absolute phase fluctuation amount
and the absolute amplitude fluctuation amount in the transmitted
signal system is detected.
FIG. 40 is a block diagram of the nineteenth embodiment of the
radio communication system according to the present invention. In
FIG. 40, the constituting parts common to FIG. 34 are denoted with
the same reference numerals, and different respects will mainly be
described hereinafter.
The base station 1 of FIG. 40 is constituted similarly as the base
station 1 of FIG. 34. In addition to the constitution of FIG. 34,
the control station 2 of FIG. 40 has a switch (control station
switch means) 176 for selecting either one of weighted transmitted
signals. The calibration coefficient calculation circuit 164 of
FIG. 40 detects absolute values of the absolute phase/amplitude
fluctuation amount of the transmitter included to the transmitted
signal by using the transmitted signal selected by the switch 176
and the output of the feedback signal detector 163 corresponding to
the same branch.
The output C.sub.Tk of the calibration coefficient calculation
circuit 164 of FIG. 40 is obtained in equation (33).
.times.e.function..theta..PHI..function. ##EQU00022##
Here, .theta.k and Ak represent the phase fluctuation amount and
the amplitude fluctuation amount of the feedback transmitted signal
(the signal is subjected to distortion of the
transmitter/receivers) of k number branch, respectively. .phi.k and
Bk represent phase fluctuation amount and amplitude fluctuation
amount of the receiver of k number branch obtained by the pilot
signal.
The weighting coefficient calculation circuit 165 of FIG. 40
calculates weighting coefficient wTk of the transmitted signal
based on the following equation (34). wTk=w'TkCTk (k=1,2,3)
(34)
In the radio communication system provided with the adaptive
antenna, when the relative phase and relative amplitude fluctuation
amount of the transmitted signal are known, a transmitted beam
pattern can be correctively formed. However, when it is necessary
to know the absolute phase fluctuation amount and absolute
amplitude fluctuation amount of each transmission branch for other
purposes, the aforementioned nineteenth embodiment is
effective.
Moreover, the nineteenth embodiment is effective when a delay time
until returning of the transmitted signal via the feedback
transmission path, that is, phase rotation is sufficiently short as
compared with one symbol length of the signal.
Twentieth Embodiment
In a twentieth embodiment, the absolute phase fluctuation amount
and absolute amplitude fluctuation amount can be detected without
any pilot signal.
FIG. 41 is a block diagram of the twentieth embodiment of the radio
communication system according to the present invention. In FIG.
41, the constituting parts common to FIG. 40 are denoted with the
same reference numerals, and different respects will mainly be
described hereinafter.
The radio communication system of FIG. 41 is characterized in that
no pilot signal is inserted, and instead there is provided an
exclusive feedback path for calibration to send the transmitted
signal from the control station 2 to the base station 1 back to the
control station 2.
The base station 1 of FIG. 41 has a switch (base station switch
means) 177 for selecting either one of the transmitted signals from
the control station 2, amplifier 178 for amplifying the signal
selected by the switch 177, frequency converter (second frequency
conversion means) 179 for converting the frequency of the signal
amplified by the amplifier 178, and electric/optical converter
(second electric/optical conversion means) 180 for converting the
output signal of the frequency converter 179 to the optical
signal.
Moreover, the control station 2 of FIG. 41 has an optical/electric
converter (second optical/electric conversion means) 181 for
converting the feedback signal of the transmitted signal
transmitted from the base station 1 to the electric signal. The
output signal of the optical/electric converter 181 is inputted to
the feedback signal detector 163.
In the radio communication system of FIG. 41, by successively
switching the switch 177 in the base station 1 and the switch 176
in the control station 2, the transmitter is calibrated by each
branch. Additionally, both the control station 2 and the base
station 1 identify the branch corresponding to the antenna element
being calibrated.
Moreover, in the radio communication system of FIG. 41, the
phase/amplitude fluctuation amount of each transmission branch are
different from one another, but the phase/amplitude fluctuation
amount of the exclusive feedback path are constantly common, and
the calibration coefficient of each branch obtained by the
calibration coefficient calculation circuit 164 is therefore
obtained as the relative value among the branches. Generally, in
the system provided with the adaptive antenna, when the relative
phase and amplitude are constant, the antenna pattern is univocally
determined, so that calibration can correctly be performed even
when neither absolute phase nor amplitude fluctuation amount is
known.
Moreover, for the calibration of the receiver in the radio
communication system of FIG. 41, by establishing the transmitter
calibration, subsequently feeding the transmitted signal back to
the control station 2 via the receiver in the base station 1, and
comparing the transmitted signal with the weighted signal with the
weighting coefficients including the transmitter calibration value
in the control station 2, the calibration coefficients of the
receiver can be obtained.
As described above, in the twentieth embodiment, since the relative
phase difference and relative amplitude fluctuation amount can be
detected without using the pilot signal, the processing of
inserting the pilot signal and performing multiplexing in the base
station 1 is unnecessary, and the processing of separating and
extracting the pilot signal in the control station 2 is also
unnecessary. Therefore, the system constitution can be
simplified.
Twenty First Embodiment
In the aforementioned eighteenth to twentieth embodiments, an
example has been described in which the weighting coefficient
calculation circuit 165 generates the weighting coefficient
including the calibration coefficient with respect to the
transmitted signal and performs the weighting of the transmitted
signal, but separately from the weighting of the transmitted signal
by the transmission weight, the weighting for compensating the
transmitter distortion by the calibration coefficients may be
performed.
FIG. 42 is a block diagram of a twenty first embodiment of the
radio communication system according to the present invention. In
FIG. 42, the constituting parts common to FIG. 40 are denoted with
the same reference numerals, and different respects will mainly be
described hereinafter.
The base station 1 of FIG. 42 is constituted similarly as FIG. 40.
Moreover, the calibration coefficient calculation circuit 164 in
the control station 2 of FIG. 42 performs the processing similar to
that of FIG. 40, but the processing result is supplied not to the
weighting coefficient calculation circuit 165 but to multipliers
(third weighting means) 182a to 182c newly disposed on the
transmitter.
Moreover, the weighting coefficient calculation circuit 165
calculates transmission and reception weights without considering
the calibration coefficient calculated by the calibration
coefficient calculation circuit 164. The multipliers 43a to 43c
perform the weighting of the transmitted signal based on the
transmission weights. Moreover, the newly added multipliers 182a to
182c further perform the weighting by the calibration
coefficients.
Additionally, also with respect to the aforementioned radio
communication system of FIG. 41, similarly as FIG. 42, the
weighting by the transmission weights may be performed separately
from the weighting by the calibration coefficients.
FIG. 43 is a block diagram of the radio communication system
obtained by modifying FIG. 41. The base station 1 of FIG. 43 is
constituted similarly as FIG. 41. Moreover, the weighting
coefficient calculation circuit 165 in the control station 2 of
FIG. 43 calculates the transmission and reception weights without
considering the calibration coefficients calculated by the
calibration coefficient calculation circuit 164. The multipliers
43a to 43c perform the weighting of the transmitted signal based on
the transmission weights. Moreover, the newly added multipliers
182a to 182c further perform the weighting of the weighted
transmitted signal based on the calibration coefficients.
As described above, in the twenty first embodiment, since the
weighting by the transmission weight is performed separately from
the calibration by the calibration coefficients, it is also
possible to perform only either one.
In the aforementioned eighteenth to twenty first embodiments, an
example has been described in which the sub-carrier multiplexing
(SCM) method is used as the transmission method in ROF, but even
with the transmission methods other than the SCM, such as a
waveform division multiplexing transmission method, a method of
allotting plural optical fibers to separate branches, a time
division multiplexing transmission method, and a code division
multiplexing method, the similar system can be constructed. That
is, the present calibration method does not depend on transmission
method when transmitting the optical fiber.
In the above-mentioned the eighteenth to twenty first embodiments,
although examples of transferring the transmitted/received signal
by FDD has been described, the same effect is obtained by the same
constitution even in case of performing a time division duplex
(TDD).
Moreover, in the aforementioned eighteenth to twenty first
embodiments, the transmission optical fiber cable may be disposed
separately from the reception optical fiber cable, but time
division duplex (TDD) or frequency division duplex (FDD) of the
transmitted/received signal is performed, so that the
transmission/reception may be performed with one optical fiber.
Furthermore, in the aforementioned eighteenth to twenty first
embodiments, an example in which the optical fiber is used as a
wire communication medium for connecting the base station 1 to the
control station 2 has been described, but even with a system in
which a coaxial cable, Ethernet cable, or the like is used, the
similar calibration processing can be obtained, and the similar
effect is obtained.
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